Hydrogeological conditions of fault structures and fissure karst water in Houjiagou-Xiquanhe area in Laiwu city are complicated. Based on systematic analysis of hydrogeological conditions, history and scale of karst collapse, the causes of karst collapse in the area have been analyzed systematically. It is showed that karst collapse mainly occurs in Houjiagou and Quanhe areas where shallow karst develops, and occurs during or after the rain in flood season every year. It is mainly caused by frequent and large fluctuation of karst groundwater (fluctuation range is 16~40m), which results in the destruction of the clay and sandy clay with a thickness of 4~15m over the shallow karst caves, and then the collapse occurs.