Abstract: Roux-en-Y gastric bypass (RYGB) is the preferred surgical procedure for obesity and type 2 diabetes mellitus (T2DM). Currently, it is controversial how long the roux limb and biliopancreatic limb should be selected during RYGB. Based on the survey of American Society for Bariatric Surgery (ASBS) (2008), the Roux limb ranged from 10 cm to 250 cm and the biliopancreatic limb ranged from 35 cm to 250 cm. The length of small bowel exclusion may affect the postoperative results.Shorter jejunum exclusion may affect the curative effect, while overlong jejunum exclusion may result in nutritional disorders, diarrhea and other complications. Under the condition of fixed jejunal exclusion,  it is worth exploring the relationship between the postoperative outcome and different parameters of small bowel exclusion. Lacking of consensus and criteria in this field, authors focused on the related references published recent years to summarize the valuable information.