The invention discloses a liquid-controlled type under-shaft savaging tool. The tool is composed of a joint, a sealing ring, a sliding sleeve, a fixing pin, a
piston, a housing, a steel bead, a slip,a mandrel, a screw, a restoring spring, a
stroke pin, a pin spring and a semi-circular button and is characterized in that the salvaging tool is connected with the lowermost part of an under-shaft
piping, and threads are tightly screwed to lower the tool into a shaft. Lowering is stopped when a lowering device is 1-2 m from the top of fish, and the total suspension weight is recorded. A
sludge pump is started to flush the fish, the
sludge pump is switched off after the fish is washed clean, and the salvaging tool is slowly lowered again. When the suspension weight is reduced, lowering is stopped to try to lift a drilling column, when it is confirmed that the fish is caught, and the salvaging tool is lifted upwards to take out the fish. If fish salvaging is blocked, tool
piping is lowered,lowering is stopped when a weight indicator is lowered than the suspension weight again, the
sludge pump is started for around 10 seconds, the
piping is lifted upwards, and the tool is taken out fromthe fish.