In Xin'anjiang model, problem of the spatial distribution of rainfall has been well resolved while other non-uniform distributions are ignored. In fact, the runoff concentration behaviors of a basin is largely depended on topographic characteristics. This paper put forward a new method, in which digital elevation model (DEM) was used to differentiate sub-basins and to extract average slope and maximum length of flow concentration which makes a positive contribution to calculate shape coefficient. On the basis of adding shape coefficient and average slope into Xin'anjiang model, the relationship between this two factors and runoff concentration parameters was established to make sure that the effects of both shape and topography can also be concerned In Xin' anjiang model at the same time. The improved model has been used to forecast floods in Yanduhe River Basin with good results being obtained.