There are low precipitation and high evaporation in Xinjiang while water surface evaporation main stem from water loss of river runoff. Agriculture is an important economic backbone in Xinjiang. However, farming need irrigation. Because canal system will lead to hihg water surface evaporation, scientific forecasting water surface evaporation is the foundation of effectively utilizing water resources and promoting agriculture development. This paper analyzes the relationship between monthly average air temperature, humidity, vapour pressure and water surface evaporation with meteorological data during thirty years in Xinjiang. The results indicate that there are close correlations with which a model can be built to forecast water surface evaporation. The model has been tested and verified with monthly temperature data. The results show that it is not only more reasonable, but also has fewer errors than the others.