Complex approach to the estimation of runoff from the small catchments is suggested which makes it possible to consider the specific features of runoff formation in the mountains. River flow modeling is based on the Hydrograph model created by Yu. Vinogradov. The object of research is the Us River drainage basin (the right tributary of the Yenisei River) located in the middle and low mountains of the West Sayan. The authors suggested the technique of pluviometric gradients calculation based on the correlation analysis of daily precipitation data for warm and cold periods. The trends of the altitudinal distribution of precipitation were revealed. Areas with similar conditions of runoff formation - runoff forming complexes (RFC) - were identified basing on the mesoscale landscape map. Quantitative characteristics of soils and vegetation cover for each runoff forming complex (RFC) were used as parameters for modeling. According to the results of modeling the convergence of calculated and observed hydrographs becomes considerably higher if the pluviometric gradients and RFC characteristics are taken into account.