Releasing overshot is one of the fishing tools which fish the pipes externally. It can catch drill collar, drill pipe, tubing, subs and other pipes. Because of the seals, the fluid can circulate with the high pump pressure after catching the fish. The top of the fish will be milled by under mill shoe. It can also work with jars to catch the stuck fishes. If the catched fish can't be released from stucking, we should release the overshot and lifting the drill string.