The invention discloses a water seal body-adjustable sizing device. The water seal body-adjustable sizing device comprises a sizing sleeve, an outer casing pipe sealedly arranged at the periphery of one end of the sizing sleeve and a water seal body axially movably connected to the outer casing pipe. An annular water outlet channel is formed between ends of the water seal body and the sizing sleeve or the outer casing pipe. Outlet water of the annular water outlet channel is continuously sprayed to the pipe outer wall surface. A first water storage cavity is formed between the outer casing pipe and the water seal body. The outer casing pipe is provided with a first water inlet for supplying water to the first water storage cavity. The water seal body can be axially adjustably installed on the outer casing pipe so that the axial width of the annular water outlet channel can be adjusted, water yield in unit time can be adjusted and a cooling capability of water sprayed by the annular water outlet channel can be adjusted and thus the water seal body-adjustable sizing device is suitable for cooling pipes having different thickness values, different pipe diameters and different temperature requirements, lays a good foundation for follow-up sizing, and has a reliable structure convenient for adjustment.