The invention discloses a method for determining the runoff relation of an underlying surface on basis of mathematical statistics. The interannual variation rule of rainfall and the interannual variation rule of runoff are analyzed by using ArcGIS and SPSS software on the basis of land information and meteorological station information, a main underlying surface factor is determined, a model of influence of underlying surface variation on runoff is established with a runoff coefficient as a dependent variable and plough, forest land, building land and other underlying surface factors as independent variables, the correlation between each underlying factor and the runoff coefficient is established, influence of underlying surface variation on runoff is quantitatively analyzed, and a linear equation and a nonlinear equation are determined; besides, the correlation between rainfall and runoff is considered, the rainfall factor is also considered while the underlying surface factor is analyzed, a statistic model with the rainfall taken into consideration is established, and a linear equation and a non-linear equation with higher relevancy are obtained.