The invention relates to a water-cooling tool for an oil tank. The water-cooling tool comprises a fixed seat (1), a clamping claw (2) and a driving mechanism, wherein the clamping claw (2) and the driving mechanism are connected to the fixed seat (1); a floating seat (3) is arranged on the fixed seat (1), and the driving mechanism and the clamping claw (2) are located on the floating seat (3); a step hole (4) is formed in the fixed seat (1), the floating seat (3) is located in the step hole (4), and an annular bulge (5) is arranged on the outer wall of the floating seat (3); a pressure ring (6) for axially limiting the annular bulge (5) is further arranged on the floating seat (3); a reset mechanism is arranged between the floating seat (3) and the fixed seat (1); a limiting baffle sheet (29) is arranged at one end, close to the clamping claw (2), of a transmission mechanism, and a pressure spring (30) is arranged between the limiting baffle sheet (29) and the transmission mechanism. Compared with the prior art, the water-cooling tool for the oil tank has the characteristics that the stability and the uniformity of the shape of a tank body of the oil tank during water cooling are relatively good, namely, the connective stability at a clamping ring of a pump hole is relatively good.