Abstract: The paper discussed the deformation mechanism of one high steep dipslope in Jinping hydropower station. Through field investigation, experimental analysis and numerical simulation, the authors have a more profound insight into the problem. The previous conclusions were discussed in the paper. There is evidence that problems exist in earlier analysis. As a result, a new insight was gained. The results indicate that the deformation of deep rock layer at Jiefanggou left bank high slope is caused by a combination of deep unloading relaxation at slope in the course of cutting valley in high terra stress area and bending-toppling of deep rock layer at high dipslope.