Reference crop evapotranspiration (ET0) is an important parameter in calculating water requirement of crops. In order to reduce the error in irrigation parameters calculation due to the differences of climate and topography of Gansu province, the area was divided into four regions(the humid area of Longnan and Gannan , the semi-humid area of south Longzhong, the semi-arid area of north Longzhong and the arid area of Hexi) according to the geographical characteristics and humidity degree to analyze the distribution and impact factors of ET0. Daily meteorological data collected from 26 national meteorological stations from 1980 to 2015 was used to calculate ET0 with FAO-56 Penman-Monteith equation, meanwhile, temporal-spatial distribution characteristics and impact factors of ET0 in Gansu province and the four divided regions were analyzed with inverse distance weighted spatial interpolation method (IDW) and partial correlation analysis method. Results showed that the interannual variation trend of ET0 in Gansu province decreased from 1980 to 1991, increased from 1991 to 2015, with an overall increase trend. The spatial distribution of ET0 in Gansu province increased gradually from southeast to northwest. Moreover, ET0 has an extremely significant positive correlation with daily maximum temperature, minimum temperature, daily average temperature, average wind speed and sunshine hours while presents a highly significant negative correlation with average relative humidity. The order of influence degrees of these parameters present a sequence of U>N>Tmax>RH>Tmin>Tmean in the whole Gansu Province, N>U>Tmax>RH>Tmin>Tmean in the humid area of Longnan and Gannan, N>U>RH>Tmax>Tmean>Tmin in the semi-humid area of south Longzhong, and U>N>Tmax>RH>Tmin>Tmean both in the semi-arid area of north Longzhong and the arid area of Hexi. Following conclusions can be made, topography and climate have a great influence on ET0, which increases from humid area to arid area. The ET0 was significantly differentiated in each area and increased from the southeast to the northwest. The main influencing factors of ET0 in Gansu Province were the average wind speed and sunshine hours.