Objective:To analysis the role of obesity in obstructive sleep apnea hypopnea syndrome (OSAHS). Methods:The differences of apnea hypopnea index (AHI), the lowest saturation of blood oxygen, the longest respiratory event and mean respiratory event between obese and nonobese patients with OSAHS were compared. The relevant influence factors including patients’ gender, age, body mass index (BMI) and obesity on the AHI and the lowest saturation were analyzed through multiple linear regression. Results:The mean AHI of nonobese group was smaller than that of obese group, while the lowest saturation of blood oxygen in nonobese group was greater than that in obese group. The differences were statistically significant. But the differences of the longest respiratory event and mean respiratory event between the two groups were insignificant. In female patients, every 1 kg/m2 increase at BMI translated into 3.058 times/min in AHI. BMI being equal, the AHI of male patients was 10.311 higher than that of female ones. For each 1 kg/m2 increase at BMI, female patients reduced the lowest saturation of blood oxygen by 1.290%. BMI being equal, the lowest saturation of blood oxygen of male patients was 4.189% lower than that of female ones. Conclusions:With the increase of BMI, the severity of OSAHS will gradually increase. BMI has stronger influence on OSAHS in male patients than that in female ones.