It is of great significance to explore the seasonal first flush phenomenon of rainfall runoff for urban water environment management and water pollution control. Based on the dimensionless handled rainwater runoff pollutants and effective rainfall，the mathematical model for quantitative evaluation the seasonal first flush effect of rainwater runoff pollutants was established. The established mathematical model was applied to investigate the seasonal first flush effect on building roof and on campus. Results showed that the relationship between the average concentration of runoff pollutants and effective rainfall is similar in the building roof and on campus. The concentration of runoff pollutants in the early and late stages of rainy season was higher than that in the middle stages of rainy season. The strength of seasonal first flush was different in the study area, and the seasonal first flush phenomenon was found significantly for SS and TN while the strength of seasonal first flush (SFF) was relatively lower for COD and TP. SS and TN are mainly controlled in spring while COD and TP are mainly controlled in spring and late autumn.