The utility model relates to a governing valve sealing performance detects technical field, specifically discloses a leak detector in water pressure formula cage type adjusting valve valve trim of nuclear power plant. A leak the detector in the water pressure formula governing valve valve trim of nuclear power plant, this detector of includes piston cylinder body, piston packaging terminal surface, closing device and manual hydraulic pump, wherein, the piston packaging face -to -face mounting is in piston cylinder body for to wait that the case, the seat kits that detect seal in piston cylinder body, be equipped with closing device on the piston packaging terminal surface, be used for applying the sealing force, be equipped with to draw on piston cylinder body lateral wall and press the pipe, draw and press the pipe other end to be connected with manual hydraulic pump. A leak detector in water pressure formula cage type adjusting valve valve trim of nuclear power plant, can effectively check the governing valve leakproofness, detect the sealed quality of its sealed face effectively, avoided the interior hourglass circumstances that the maintenance back has resulted in because the sealing force is not enough.