According to the characteristics of medium - and small -sized basins in Heilongjiang Province, this paper took the 4 basins of Yantongshan, Tieli, Chanlinheqiao, Zhonghe as the study areas, and introduced initial abstraction proportion m and deviation factor of the system k to modify the SCS model. This paper discussed the feasibility of the modified SCS model in the simulation of rainfall-runoff relationship of study areas. The results show that the efficiency coefficients of the modified SCS model are all above 0.80, and this model can be used in Heilongjiang Province to simulate the rainfall-runoff relationship, which shows a good simulation result.