Abstract: In order to solve the safety problem of fully mechanized caving mining under the compound water body composed of goaf and ground subsidence water, the II3 extra-thick coal seam in the first mining area of Linglu Coal Mine is faced by the II2-1 coal seam mined water and ground subsidence water. Take the mining under the composite water body as an example. Using the method of combining engineering analogy and theoretical analysis, the damage height of the overlying strata in fully mechanized caving mining, as well as the height of the coal and rock pillars for waterproof, sand control and collapse prevention are calculated; The difference between the distance between the water area and the mining coal seam and the height of the safe coal rock pillar, using the Kriging difference method to draw three maps of the influence of the water in the goaf on the water filling, sand break and collapse prevention of the mining coal seam. Comprehensively analyzed the threat of the roof composite water body in the first mining area II3, and finally evaluated the safety of fully mechanized caving mining under the composite water body. The research results show that: mining in a mining area can meet the requirements for water-proof and safe coal and rock pillars in surface subsidence water; fully-mechanized caving mining in extra-thick coal seams under surface subsidence water is safe; combined geophysical prospecting and drilling to determine the mined-out area volume After the water has been drained, the safe mining of the submerged water in the goaf can be realized; after the composite water body is taken to leave safe coal and rock pillars, combined with geophysical and drilling, and carry out comprehensive water prevention and control measures such as drainage of the water in the goaf, Fully mechanized caving mining under complex water bodies is safe and feasible.