The utility model relates to a structure prefab turning device under subway and the railway tunnel rail, specifically be a structure prefab upset machine under rail, install two -way hoist engine and two supports on its base, all be fixed with bearing on the support, be equipped with the bearing in the bearing, the roll -over stand includes the bottom surface board, the side board, the both sides arm -tie, be equipped with bottom surface height -adjustable support on the board of bottom surface, be equipped with cambered surface height -adjustable support on the board of side, the central point of side arm -tie puts and is equipped with the rotation axis, the rotation axis is installed in the bearing, wire rope one end on the two -way hoist engine is connected with the side board outside of roll -over stand, the other end is connected outside fixing the reverse back of fixed pulley and the roll -over stand bottom surface board on the base, still be provided with forward limit switch and reverse limit switch on the base. The utility model has the advantages of reasonable design reliably, have the upset highly low, required moment is little, energy saving, structure are simple relatively, reliable operation, the operation of easily maintaining, be convenient for, advantage that the cost is low.