Taking bare Pisha Sandstone slope as the research object, based on the field runoff plot scouring test and three-dimensional laser scanning technology, the evolution of rill micro morphology and erosion sediment yield mechanism on Pisha Sandstone slope were studied under combined erosion with three kinds of flow (60, 100 and 200 L/h) and four slopes (5°, 10°, 20° and 30°). The results showed that the rill developed first at the bottom of the slope and then extended upward with the increasing of scouring flow and slope gradient. The occurrence time of rill decreased with the increasing of slope gradient. The rill shape was "wide and shallow type" on the slope less than 10°, the maximum width to depth ratio was 0.038. While the rill shape was "deep and narrow type" on the slop more than 20°, the minimum width to depth ratio was 0.038. With the increasing of erosion intensity and slope gradient, the ratio of rill width to depth became smaller, while the number, density, complexity and fragmentation of rill increased. Slope gradient and scouring intensity affected the change of slope sediment yield together. With the increasing of slope gradient and scouring intensity, the sediment yield increased first and then decreased. There was a significant negative correlation between ratio of rill width to depth and slope sediment yield (-0.935, P<0.01), and a significant positive correlation between rill density, rill fragmentation and sediment yield (0.888, 0.944, P < 0.01).