Abstract: Based on the meteorological data derived from the national “863” special project, relationship between reference evapotranspiration(ET0) and the effected factors was analyzed. Net radiation (Rn) and vapor pressure deficit (VPD) were selected as influence factors to construct the regressive formula to calculate ET0. Then the influence of wind was considered. Results show that: Rn is the greatest influence factor, following by VPD, sunshine hour (N) and temperature (T). Liner relationship is found between ET0 and Rn or VPD, exponential relationship between ET0 and N or T, and negative relative relationship to relative humidity (Rh). Simplified fomular modified by wind can get great coherence with Penman-Monteith method commended by FAO.