The calculation method of regional land surface evaporation is based on the adequate absorbing previous achievements. In this method the research region is classed as: urban area, mountainous area and plain area by analyzing the different conditions of the underlying surface, planting covering rate and water supplies. Each kind of area is divided into sub areas such as water body, water leakage area and non-water leakage area and its evapotranspiration is calculated. The total evaporation of each kind of area can be got by integrating the value of its sub areas. Thus, with the evaporation calculation of urban area, mountainous area and plain area as the sub model, a calculation model for regional synthetic evapotranspiration is created.