The utility model discloses a moisture absorber for an oil-immersed power transformer, which can finish oil liquid adding and supplementing operations without completely detaching a small purificationchamber, can visually find the position of an oil surface, and is simple and easy to operate and high in working efficiency. The air purifier comprises a large purifying chamber and a small purifyingchamber, the top end of the large purification chamber body is connected with a transformer box body pipeline through a sealing plate and a connecting flange; a filling port is formed in the lower end of the connecting flange; moisture absorption materials in the large purification chamber are injected through the material injection opening. A window is arranged on the large purification chamber,the filling amount and the use condition of moisture absorption materials in the large purification chamber can be observed through the window, a discharging port is formed in the lower portion of the large purification chamber and used for replacing the moisture absorption materials, the bottom end of the large purification chamber is connected with the small purification chamber through a flange, and an oil filling port is formed in the upper portion of the small purification chamber and used for filling oil. The utility model can be widely applied to various types of oil-immersed power transformers.