It is important for regional agricultural production as well as water resources planning and management to better understand the spatial and temporal variations of potential evaporation (PET) and their possible causes from a perspective of climate change. In this study, the spatial and temporal changes in monthly and annual PET covering 1960 similar to 2006 in the Wei River Basin (WRB), a typical arid and semi-arid region in China, were thoroughly examined based on the modified Mann-Kendall trend test method. Additionally, the slope change ratio of accumulative quantity (SCRAQ) method was used to quantify the effects of precipitation, air temperature, percentage of sunshine, and wind speed on PET variations. Results indicated that: (1) the PET in this basin gradually increased from west to east, which had general negative correlations with its corresponding elevation; (2) the WRB was dominated by increasing monthly PET, and obviously decreasing tendencies were observed in summer in the middle basin; (3) the decreasing PET in 1974-1993 in the whole basin was primarily caused by the decreasing percentage of sunshine, whilst the increasing PET in 1994-2006 is mainly induced by the upward air temperature in the WRB.