The utility model provides a tool for testing the sealing effect of a cable drum. The device comprises two clamping plates and a fixing frame, the two clamping plates are oppositely arranged and connected through the fixing frame, the clamping plates are provided with fence parts capable of being attached to the outer side wall of a cable drum, and the fence parts of the two clamping plates definea containing cavity with an upper opening and a lower opening when folded. According to the utility model, the accommodating cavity formed by enclosing the clamping plates when the clamping plates are folded is arranged, and whether water leaks from the bottom of the cable drum is detected after water is stored in the accommodating cavity during detection, so that the sealing effect of the cabledrum can be accurately detected, wrong detection is not easy, the working efficiency is improved, water resources are saved, waste is avoided, and the economic cost is reduced.