Based on the observational data of 47 meteorological stations in the northern and southern regions of the Qinling Mountains (NSQ) during 1960–2012, this paper estimated the potential evapotranspiration (ET0) by using the Penman–Monteith method. Further, a quantitative study was conducted of the ET0 spatial distribution pattern, temporal variation rules, influencing factors and attributions. The conclusions were as follows. (1) The spatial distribution of annual ET0 in NSQ decreased from northeast to southwest. The seasonal distribution was summer > spring > autumn > winter. (2) Further, 1979 and 1993 were the turning points of the ET0 trend, at which the value began to decrease or increase over the whole region and sub-regions. At the seasonal scale, in the period of 1960–1979, ET0 in spring, summer, and winter presented a decreasing trend; however, it increased slightly in autumn. During 1980–1993, ET0 in most seasons showed a downward trend except for autumn; in the period of 1994–2012, ET0 declined in summer and autumn, however it increased slightly in spring and winter. (3) The diurnal temperature range during 1960–1979 contributed most to ET0. The decrease of wind speed and solar radiation were the main cause of the ET0 decrease during 1980–2012, which offset the effect of the increase in temperature.