Background: A meta-analysis of published cohort studies was used to evaluate differences in outcome measures after total knee arthroplasty (TKA) among thinnish, normal, overweight, obese, and morbidly obese patients. Materials and methods: Manual retrieval of the results of patients with different body mass index (BMI) in primary TKA from the self-built Chinese and English databases such as PubMed, EMBASE, Cochrane, Sinomed, CnKI, Wanfang, and Vip from November 2020 was performed. Include retrospective or prospective cohort studies, according to the World Health Organization BMI packet primary TKA special surgical hospital in New York, the knee joint function assessment used in patients with knee scoring criteria (HSS) or the knee society score (KSS) as well as the operation time, intraoperative blood transfusion volume, length of hospital stay, postoperative complications of literature, literature including repeat, system evaluation, meta-analysis, case report, BMI groups not strictly and outcome indicators of incomplete documents. After independent literature screening, data extraction, and quality evaluation by 2 researchers, meta-analysis was carried out with Revman5.4 software. In the end, 20 literatures were included. Results: The preoperative score decreased with the increase of BMI in each group, while the postoperative knee joint function score in the normal group, overweight group, obese group, and in the morbidly obese group were all higher than that before the surgery (P<0.00001), and the changes were more obvious in the morbidly obese group. The length of stay in the normal group was the shortest, followed by the overweight and obese group. The operative time and intraoperative blood transfusion showed that the thinnish group was less than the normal group, while the overweight and the obese group was higher than the normal group. Finally, postoperative complications in the other groups were all higher than the normal group, with significant differences. We can see the preoperative knee function score decreased with the increase of BMI, the operation time, intraoperative blood transfusion volume, length of hospital stay, presents the opposite trend, the postoperative complications in each group were higher than in normal group, here also pay special attention to thinnish group compared with normal group complications increase. Conclusion: The present meta-analysis demonstrated that BMI higher than normal can affect intraoperative risk of TKA and postoperative recovery, and increase the risk of complications.