objective To analyze the impact of body mass index (BMI) on medical and surgical complications of colorectal cancer patients served by West China Hospital, based on the current version of Database from Colorectal Cancer (DACCA). Methods The data of DACCA was updated on September 27, 2021. The data included BMI, surgical complications, liver nodules, liver function, renal nodules, renal function, operation history, medical complications, diabetes, hypertension, pneumonia, pulmonary nodules, pulmonary function, heart disease, thrombosis, and cardiac function. Results After scanning, 5 305 data rows were included. BMI was divided by Chinese four classification methods. The analysis results showed that in terms of surgical complications, obese patients were more likely to be complicated with surgical complications of digestive system (χ2= 43.883, P<0.001) and reproductive system (χ2=13.139, P=0.004). Lean patients were more likely to have surgical complications of urinary system (χ2=223.415, P<0.001), and obese patients had liver function (H=61.521, P<0.001) and renal function (H=9.994, P=0.019) might be even worse. In terms of operation history, BMI in colorectal cancer patients had nothing to do with the number of times of operation (H=6.262, P=0.100), and operation history of each system or department (P>0.05). Regarding to medical complications, with the increase of BMI, the risk of colorectal cancer patients with diabetes mellitus (χ2=118.597, P<0.001), or hypertension (χ2= 163.334, P< 0.001) increased. Patients with low BMI were more likely to have pneumonia (H=7.899, P= 0.048) and worse pulmonary function (H=40.673, P<0.001). Conclusions The analysis results of DACCA database show that BMI is not related to the occurrence of any special surgical history included in the research. Because the internal and external complications of patients are closely related to the treatment plan and prognosis, we should pay more attention to the obese patients in the process of clinical treatment, and they are more likely to have multisystemic abnormalities and various abnormal indicators than other patients. For thin patients, we should pay more attention to their lung function and inflammatory lesions, so as to improve the clinical therapeutic effect.