In order to make full use of the dam body covering resources of Taipingsi Reservoir in Longdongwan Mine, Matlab was used to predict the deformation value of surface deformation according to the occurrence of coal seam, water-separation and surface water body characteristics, and it was controlled by sapphire strip and staggered filling method. The displacement of the roof ensured the safety of the dam body, effectively utilized the dam body crushing resources, changed the traditional room-column mining method with low resource recovery rate, and realized the coal-free column mining and the actual recovery rate of coal mining under water. It reached 90.5% and provided reliable guarantee for mine safety production, effective use of resources and environmental protection.