Abstract: In this paper, temperature changes and precipitation fluctuations over Songnen Steppe since are analyzed 1953. Based on a soil water balance model and a climate yield empirical model, the impacts of recent forty years and future changes of temperature and precipitation on soil water and grassland productivity are estimated. Over forty years, winter and spring temperature have increased by 2.0℃ or so; autumn and annual temperature have increased about 1.0℃; summer temperature increased by 0.2℃. There is not a trend in precipitation changes. The impacts of temperature increase since 1953 on soil water and grass yield are small, the changes of soil water and grass yield are mainly dependent on precipitation changes. In CO₂ doubling situation, according to GISS and GFDL GCMS outputs, temperature will increase by 3-6℃ and precipitation increase about 10% over Songnen Steppe. Such changes in temperature and precipitation will result in soil water decrease every month, while evapotranspiration will increase during rain season. Grass yield will decrease by 3%-4%.