Abstract: Aiming at mining of Yonghua Energy NO.1 coal mine under reservoir, it not only needs to ensure the safety in production, but also needs to ensure the normal operation of the reservoir. First, the damaged height of the overlaying strata was analyzed after coal working face mined under ZhaoCheng reservoir area. And then influence of the mining under reservoir on the reservoir safety was analyzed through the dam deformation failure, dam cracks, dynamic movement and deformation which caused by mining. The results showed that water flowing fractured zone of each calculation point in area of the reservoir did not spread to the Zhaocheng reservoir, so the mining under reservoir was safe. Mining in No.22 mining area would not damage the dam, but might cause dam cracks and the corresponding processing methods was put forward. Finally, according to the geological and mining conditions, reasonable mining speed was proposed.