Abstract： Objective:To analyze the correlation between the body composition and cardiorespiratory fitness (CRF) decline in physical examination population of different genders.Methods:Clinical data of the cardiopulmonary exercise testing (CPET) and body composition analysis of 439 people who received physical examination in the Medical Examination Center of Peking University Third Hospital from May 2021 to September 2021 were retrospectively analyzed. The general data, physical examination, biochemical parameters, body composition and CPET results were collected. The subjects were divided into normal group and decline group according to the percentage of peak oxygen uptake (VO 2peak) levels ≥ 85% or<85%. Multivariate logistic regression was applied to investigate the influencing factors of CRF decline in subjects of different genders. Results:Among men, total cholesterol and triglyceride in the decline group were significantly higher than those in the normal group [(5.097±0.890) vs (4.865±0.856) mmol/L, (1.778±1.200) vs (1.485±0.709) mmol/L], and the blood homocysteine (Hcy) and skeletal muscle index were significantly lower than those in the normal group [13.00 (11.30, 15.90) vs 13.80 (12.05, 17.10) μmol/L, (7.89±0.65) vs (8.08±0.64) kg/m 2] (all P<0.05). Among women, skeletal muscle index in the decline group was significantly lower than that in the normal group [(6.21±0.52) vs (6.53±0.56)kg/m 2], and percent body fat was significantly higher than that in the normal group [(32.83±4.92)% vs (31.21±4.55)%] (all P<0.05). The elevation of triglyceride level ( OR=1.487, 95% CI: 1.042-2.121) and visceral fat area ( OR=1.032, 95% CI: 1.014-1.051) were positively correlated with the decline of CRF in man, the decrease of skeletal muscle index ( OR=0.215, 95% CI: 0.106-0.435) and the increase of percent body fat ( OR=1.149, 95% CI: 1.060-1.245) were positively correlated with the decrease of CRF in women (all P<0.05). Conclusions:There is a correlation between body composition and CRF decline in physical examination population of different genders. Men should control visceral fat more effectively, and women should pay attention to increase muscle mass while reducing body fat, in order to improve CRF.