Abstract: By using the meteorological and hydrological data in 1971-2012 and the AdvectionAridity model which is based on the complementary relationship method, this paper studied the spatiotemporal variation of actual evapotranspiration (ET_a) and related affecting factors in the second tributary of the Songhua River basin, China by the linear trend analysis, MannKendall rank correlation analysis, Inverse Distance Weighted interpolation method, and Pearson’s correlation coefficient. In the second tributary of the Songhua River basin, the average annual actual ET_a was 435.99 mm. The actual ET_a in 1971-2012 had a significant increasing trend with a rate of 11.82
 mm·10 a^-1, and showed a complementary relationship with the decrease of potential evapotranspiration. The increase of the actual annual ET_a in spring, summer, and autumn had an obvious contribution to the increase of yearly actual ET_a. There were two centers of high ET_a in south area (540.7 mm) and north area (461.1 mm), and one center of low ET_a (223.0 mm) in the central part of Jilin City. The actual ET_a in the whole basin showed a consistent increasing trend, but the confidence was higher in northern basin than in southern basin. The increase of average air temperature, maximum air temperature, minimum air temperature, atmospheric pressure, and actual water vapor pressure in this basin caused the increase of the radiation-energy item, and then, caused the increase of the ET_a. The decrease of wind speed and the increase of actual water vapor pressure contributed more to the decrease of the aerodynamics item, and the final effect was to accelerate the increase of the ET_a.