The instantaneous unit hydrograph method for calculating rainstorm flood is widely used in China.The original parameters of the instantaneous unit hydrograph method,such as geographical parameters,runoff yield and concentration parameters and rainstorm parameters,often have certain error,which will cause corresponding error in the surface runoff process through error propagation.By expanding the basic equation of the instantaneous unit hydrograph method with the first-order Taylor′s Formula of multivariate function,the error propagation equation with the first-order algebraic accuracy of each parameter can be obtained.The results show that the relative error propagation of rainstorm has a certain amplification effect;The relative error of watershed area will lead to the equivalent relative error of surface runoff process;The relative error propagation sensitivity of infiltration quantity is relatively small overall,and may still be large locally;With the increase of parameters N and K,the peak value of surface runoff will decrease,the rising section will be flatter and thinner,and the falling section will be plumper,and there is an insignificant trend in the occurrence of peak time moving backward.