In order to provide a scientific and reliable basis for water management and optimization, a distributed hydrological model (SWAT) was applied to the runoff simulation of the Yuncheng reach of the Fenhe River. Firstly, based on the available data, the relationships between runoff and precipitation were explained from both time and space by simulating the runoff of the study area. Secondly, by use of the method of incremental scenario, different climate scenarios were assumed according to the possible changes of the future climate. Then, the SWAT model was used to simulate the runoff under different climate scenarios of the study area. The analysis results show: (1)the runoff distribution was consistent with the precipitation in both time and space; (2) there was a negative correlation between the annual runoff and temperature, and a positive correlation between the annual runoff and precipitation. Compared with the temperature changes, the precipitation changes played a more important role in the runoff of the study area; (3) the runoff changes of the study area showed a tendency of seasonal variation. The runoff variation reached the maximum in the flood season (from July to October) and the minimum in the dry season (from November to March); (4) the runoff of the survey area will increase with the future climate change. The runoff of the Hejin hydrological station will increase by 129 million m~3 when the temperature increases by 0.5℃ and precipitation increases by 10%.