This paper presents the results of modeling of the river runoff for the Ob-Irtysh basin using the climate runoff model in the XXth and XXIst centuries. This model is a linear reservoir one. The flow of water is divided into the surface runoff, the river flow and the groundwater flow. The model takes into account the influence of marshes and lakes depending on the percentage in a cell. The input data for the model are: precipitation, evaporation, melting of snow and temperature of the surface. For calculation of the discharge in the XXth century the reanalysis data ERA40/ECMWF and MERRA/NASA were used. For verification of the results, the data of the gauging stations on the rivers Irtysh and Ob were used. Possible changes in the hydrological regime of the discharge in the XXIst century are calculated based on the data of the CNRM/France model.