Understanding the runoff water quality and first flush effects can guide the management of urban runoff pollution.Six rainfall events were monitored and event mean concentration(EMC) and event pollutant loads per unit area(EPL) were calculated in the upstreams of Tangxi River. The M(V) curve was used to show the first flush effects. The results showed that the EMC of suspended solids(SS), chemical oxygen demand(COD_Cr) and total phosphorous(TP) were relatively large in rainfall runoff. The EMC of SS has the most significant fluctuations. There was a positive correlation beween total nitrogen(TN), TP, COD_Cr and SS. The EMC of TN was negatively correlated with the rainfall. The EPL of runoff water pollution has a positive correlation with the rainfall characteristics. Approximately 10.38 t TN, 2.29 t TP, 1022.43 t SS, 161.70 t COD_Cr and 5.18 t NH₃-N were input into the Lake Chaohu via runoffs in June, July, and August, 2015.Rainfall and antecedent dry weather period were the main influencing factors of the urban storm runoff pollution. Five kinds of pollutants had their own first flush effects, employing the FF50>50 as the standard, the magnitude of the first flush effect was SS>COD_Cr > TP > TN > NH₃-N. There was no correlation between the magnitude of first flush and rainfalls. The rainfall pattern could have a strong effect on the first flush effect. It is recommended to closure the runoffs when the rain intensity reaches to 1.36 mm/h, i.e. the runoffs begin to converge with the duration of 440 min,and the maximum intercept runoff amounts is 224319.14 m³.