Abstract: Guizhou is located in the mountain area of the Yunnan-Guizhou Plateau, with the special geographical position and high mountains and steep slopes. Widely distributed carbonate rocks lead to strong karstification, thus cause a large number of slope geological disasters controlled by strong karstification. This paper takes the Xinzhai collapse of Huishui County as a typical example of gently counter-inclined bedding slope in karst area. With the detailed field investigation and discrete element numerical simulation to explore the deformation-failure mechanism. Result shows that the slope controlled by gently counter-inclined and soft and hard layers structure with strong karstification. The slope occurs a concave cavity with the differential dissolution and then makes falling and toppling failure. Along the continuing process of the role of karst and water, the concave cavity expands and the structure plane extends further. Also the slope gradually has an expansion deformation from shallow to deep, finally results in large scale integrity sliding-destruction underlying soft rock. The deformation-failure mechanism is a collapse with periodical characters of differential dissolutionfalling and topplingcreeping and crackingsliding out.