Abstract: Based on monthly meteorological data from 1992 to 1996 of Kuche, Shaya, Xinhe meteorological Stations in Weigan river basin, monthly reference crop evapotranspiration is calculated by Penman (FAO) Equation. Characteristics of reference crop evapotranspiration are analyzed. Meanwhile, empirical relationship between reference crop evapotranspiration and other meteorological factors are established. The results show that (1) In the unfreezing period the average daily reference crop evapotranspiration are 3.78～4.13 mm/d, 3.63～3.87 mm/ d, 3.43～3.97 mm/d in Kuche, Shaya, Xinhe county respectively; The annual variation is not great. (2) The maximum of reference crop evapotranspiration occurs in June or July, which is about 5.32～6.17 mm/d. The minimum of that occurs in October, which is about 0.89～1.45 mm/d. Monthly variation is great. (3) In March or April or October, aerodynamic term is greater, the wind speed is the main factor affecting the reference crop evapotranspiration; in May to September radiation term is greater, the radiation is the main factor affecting the reference crop evapotranspiration. (4) The relationship between monthly reference crop evapotranspiration and monthly average air temperature is linear during monthly average air temperature raises, and is exponential during monthly average air temperature drops. (5) The relationship between reference crop evapotranspiration and water surface evaporation is linear, its proportion coefficient is about 0.54. (6) The relationship between reference crop evapotranspiration and saturation deficiency is linear during monthly average air temperature drops, and is logarithmic during monthly average air temperature raises. (7) Empirical relationship between reference crop evapotranspiration and air temperature and that between reference crop evapotranspiration and 20 cm pan evaporation and that between reference crop evapotranspiration and saturation deficiency can be used in the estimation of reference crop evapotranspiration in a simple way with preferable accuracy. The results can also be used for the study of crop water consumption in this distract.

Key words: Weigan river irrigated area, reference crop evapotranspiration, Penman（FAO） equation, water surface evaporation, air temperature, saturation deficiency