Abstract: Potential evapotranspiration (ET₀) variation has great effect on the hydrological cycle and energy balance. Based on Penman-Monteith equation and rectified radiation model, ET₀ was calculated by using annual monthly meteorological data of 18 stations in the source region, and temporal variation and spatial distribution of ET₀ during 1961- 2012 were analyzed, and dominant factors affecting temporal variation and spatial distribution of ET₀ were studied. The main conclusions were as follows: annual average ET₀ ranged between 732.0-961.1 mm, and average in regional scale was 836.9 mm. Distribution pattern was as follows: ET₀ was high in northeast and southwest, low in the central part. Distribution pattern of ET₀ in summer and in autumn were similar with the annual. From 1961 to 2012, the average annual trend of ET₀ increased at a rate of 0.69 mm/a. The trend of summer increased at a rate of 0.17 mm/a, which was the main part of annual increase in the region. Spatial difference of relative humidity, the maximum temperature and radiation led to differences in the distribution of ET₀, and contribution rates of the three factors were separately 59.8%, 22.2% and 14.4%. Rising of maximum temperature, increasing of radiation and decreasing of relative humidity resulted in increasing trend of annual ET₀ in this region, the contribution rate of the maximum temperature was 56.9%, radiation was 35.6%, and relative humidity was 2.7%. There were some differences in different areas on factor combinations and the contribution rate of the factors. Wind speed factor had low effect on annual ET₀ in this region, which was one of the characteristics distinguished from other regions in our country.