Abstract: Objective To establish the optimal models among moderate-to-vigorous, vigorous physical activity and body composition in university student to find the effective physical activity level which can improve the university students' body composition. Methods Accelerometer was used to monitor physical activity of university students for 7 days in Tianjin. The body composition of the subjects was obtained by Inbody 520. Curve fitting was used to build models between the duration of moderate-to-vigorous, vigorous physical activity and FFM and PBF in university students. The optimal model was obtained according to the principle of maximum Adj. R2 value and minimum AIC value. Results The daily duration of moderate-to-vigorous, vigorous physical activity of male university students were 25.7 and 10.2 minutes, respectively, those for female university students were 20.2 and 6.6 minutes, respectively. The overweight and obesity rates of male university students were 22.9% and 22.3%, respectively, those for female university students were 17.9% and 7.6%, respectively. The percentage of body fat was negatively related to the time for moderate-to-vigorous and vigorous physical activity, while lean body mass was positively correlated to the time. Among the five kinds of fitting curves, only linear, quadratic and cubic equations had significant difference. And cubic, quadratic equation could meet the minimum AIC value and maximum Adj. R2 value for males, females, respectively. Conclusion The optimal curve between the duration of moderate-to-vigorous, vigorous physical activity of males and their FFM and PBF were shown as all cubic equations during early adulthood, while those of females were shown as quadratic equations. Increasing the duration of moderate-to-vigorous, vigorous physical activity may reduce the risk of obesity.