Abstract: Firstly, the Shanxi formation coal seam sections and hydrogeological features were analysed in research coal field. Based on the engineering geological characteristics of the thin bedrocks, the failure of the overburden during coal mining were characterized by applying comprehensive research method combining engineering geological mechanical model test and finite element numerical simulation. The development height of caving zone and water flowing fractured zone of difference thickness of coal seam were calculated under the conditions of thin bedrocks. When the mining thickness was more than 3.5m, the water flowing fractured zone reached the Quaternary bottom aquifer in different degree, and the bottom clay layer appeared fracture. These would have effect on the safety mining. The appropriate measures on prevention and cure of water were submitted purposefully, which has been confirmed by the field tests and assured that no water-intrusion hazard or sand rush would occur.