In this paper, based on the meteorological data of the eight weather stations in Taizi river basin from 1960 to 2005, monthly reference evapotranspiration(ET₀) was calculated by the Penman-Montieth formula, the characteristics and trend of ET₀ and meteorological factors changed with year and month were analyzed, and the main factors affected ET₀ were discussed with statistic method also. The results show that the ET₀ in the Taizi river basin is decreased slowly over the past 46 years. The ET₀ in May and June is the highest and that of in January is the lowest in the year. The sequences of the main factors affected ET₀ are sunshine time, wind velocity, temperature and relative humidity.