Abstract: The steep coal seam mining under water body is a technical difficult problem. Because it will bring many mining hazards such as ground subsidence, roof water inrush and water body destruction. To solve these problems in Tongjiaowan mine, the method combining with strip mining and backfilled mining is proposed. First the coal seam is divided into several strips along the trend and the width between two strips is ten meters. Then the coal seam of every strip is caved in turn from up to down. After mining every strip, the mined-out area is filled with filling materials immediately. The example simulation results show that the strip mining method is feasible and the filling effect of high strength filling material is the best. This research may be a better suggestion on resolving the problem of the steep coal seam mining under water body. The study method would also be a reference for other kinds of mining conditions including mining beneath buildings or railways.