The integrated stereo measurement of the sky and earth with UAV as the main body provides favorable conditions for the accurate and rapid measurement of the earth’s surface.When the UAV takes an orthophoto, the steep slope affects the shooting angle, which may affect the accuracy of the three-dimensional measurement of the surface.In this study,three typical farmland gullies,which were active gully (BG),stable gully (MG) and ephemeral gully (SG), were chosen to investigate the effect gully bank slope gradients on SfM-DSM error. The surface DSM (digital surface model) was obtained by using three-dimensional laser scanning (TLS) and structure from motion (SfM) methods. The elevation error of slope to the DSM of SfM was analyzed based on the DSM of TLS. The results show that: (1) The elevation error increased exponentially with the slope of gully wall, and the fitting degree was good (P value was less than 0.000 1, R² was greater than 0.80). The inflection point appeared near 60°, when the slope was less than 60°, the variation range of elevation error was 0~10 cm, and when the slope was more than 60°, the elevation error increased sharply to 10~60 cm. (2)The more active the gully was, the larger the slope ratio was, and the higher the proportion of elevation error was concentrated in the range of larger slope. For the developing gully of BG, about 75% of the elevation error was concentrated between 15° and 75°.For the stable gully of MG, about 66% of the elevation error was concentrated between 0 and 60°. For the ephemeral gully of SG, about 54% of the elevation error was concentrated between 0 and 40°.