Abstract: Objective　To investigate the clinical efficacy and prognosis of simultaneous resection of synchronous colorectal liver metastasis in patients admitted in different phases. Methods　The retrospective cohort study was conducted. The clinicopathological data of 346 patients who underwent simultaneous resection of synchronous colorectal liver metastasis in the First Affiliated Hospital of Naval Medical University (Changhai Hospital of Shanghai) from January 2000 to April 2021 were collected. There were 217 males and 129 females, aged (58±12)years. Patients under-went simultaneous resection of synchronous colorectal liver metastasis. Observation indicators: (1) clinicopathological features of patients with synchronous colorectal liver metastasis in 2000?2010 and 2011?2021; (2) surgical and postoperative situations of patients with synchronous colorectal liver metastasis in 2000?2010 and 2011?2021; (3) analysis of prognosis of patients with synchro-nous colorectal liver metastasis in 2000?2010 and 2011?2021. Follow-up was conducted using telephone interview or outpatient examination to detect survival of patients. The follow-up was performed once every 3 months, including blood routine test, liver and kidney function test, car-cinoembryonic antigen (CEA) test, CA19-9 test, abdominal B-ultrasound examination, and once every 6 months, including chest computed tomography (CT) plain scan, liver magnetic resonance imaging (MRI) and/or CT enhanced scan, abdominal or pelvic MRI and/or CT enhanced scan, within postoperative 2 year. The follow-up was performed once every 6?12 months within postoperative 2?5 years including above reexaminations. Electronic colonoscopy was performed once a year after operation. The follow-up was up to November 12, 2021. Measurement data with normal distribution were represented as Mean±SD, and comparison between groups was conducted using the t test. Measurement data with skewed distuibution were represented as M(range). Count data were described as absolute numbers, and comparison between groups was conducted using the chi-square test. Comparison of ordinal data was conducted using the rank sum test. Kaplan-Meier method was used to calculate survival rates and draw survival curves, and Log-Rank test was used to conduct survival analysis. Results　(1) Clinicopathological features of patients with synchronous colorectal liver metastasis in 2000?2010 and 2011?2021. Of the 346 patients, 59 cases underwent simultaneous resection within 2000?2010 and 287 cases underwent simultaneous resection within 2011?2021. The gender (males and females), cases with or without fundamental diseases, cases with the number of lymph nodes harvested in primary lesion as <12 or ≥12, the tumor diameter of primary lesion, the tumor diameter of liver metastasis lesion, the number of liver metastasis lesions, cases with or without preoperative treatment, cases with or without postoperative treatment, cases with adjuvant therapy as perioperative treatment, surgery or other treatment were 47, 12, 36, 23, 19, 40, (5.5±2.4)cm, (2.1±0.7)cm, 1.6±0.5, 59, 0, 16, 16, 0, 16, 43 in patients admitted in 2000?2010, respectively. The above indicators in patients admitted in 2011?2021 were 170, 117, 121, 166, 58, 229, (4.2±2.0)cm, (3.0±2.0)cm, 1.9±1.4, 208, 79, 34, 235, 74, 29, 184, respectively. There were significant differences in the above indicators between patients admitted in 2000?2010 and 2011?2021 (χ2=8.73, 7.02, 4.07, t= 4.40, ?6.04, ?3.10, χ2=21.05, 28.82, 26.68, P<0.05). (2) Surgical and postoperative situations of patients with synchronous colorectal liver metastasis in 2000?2010 and 2011?2021. Cases with surgical methods as complete open surgery or laparoscopy combined with open surgery, the operation time, time to postoperative initial liquid food intake, cases with or without postoperative complications, cases with postoperative duration of hospital stay as ≤10 days or >10 days were 58, 1, (281±57)minutes, (5±1)days, 33, 26, 14, 45 in patients admitted in 2000?2010, respec-tively. The above indicators in patients admitted in 2011?2021 were 140, 147, (261±82)minutes, (3±1)days, 233, 54, 198, 89, respectively. There were significant differences in the above indicators between patients admitted in 2000?2010 and 2011?2021 (χ2=49.04, t=2.24, 7.53, χ2=17.56, 26.02, P<0.05). There was no death in the 346 patients. (3) Analysis of prognosis of patients with synchro-nous colorectal liver metastasis in 2000?2010 and 2011?2021. Of the 346 patients, 295 cases were followed up for 47(range, 1?108)months. Of the 29 patients admitted in 2000?2010 who were followed up, there were 27 cases died. The median survival time, 1-, 3-, 5-year overall survival rates, 1-, 3-, 5-year disease free survival rates of patients admitted in 2000?2010 were 18.0 months (95% confidence interval as 12.7?23.3 months), 82.8%, 11.5%, 3.8%, 53.6%, 8.3%, 4.2%, respec-tively. Of the 266 patients admitted in 2011?2021 who were followed up, there were 109 cases died. The median survival time, 1-, 3-, 5-year overall survival rates, 1-, 3-, 5-year disease free survival rates of patients admitted in 2011?2021 were 54.0 months (95% confidence interval as 38.1?70.4 months), 93.3%, 61.8%, 47.0%, 68.2%, 33.7%, 28.3%, respectively. There were significant differences in overall survival rate and disease free survival rate between patients admitted in 2000?2010 and 2011?2021 (χ2=47.57, 9.17, P<0.05). Conclusions　With the increase of the operation volume of simultaneous resection of synchronous colorectal liver metastasis, the operation time, time to postoperative initial liquid food intake, postoperative duration of hospital stay and postoperative complications have significantly decreased, while the overall survival rate and disease free survival rate have significantly increased.