The utility model relates to a nuclear power station maintenance technical field, concretely relates to nuclear power plant's gate valve is at linear sealing test tool, the purpose is for the leakage rate and the maintenance circumstances after, before effectively examining the valve to examine and repair on line, guarantees repairing quality, effective change state that results in because of repairing quality is unqualified that reduces, the thing of extension time limit for a project takes place. Its characterized in that: it includes valve 1, valve 2, manometer and suppresses the platform, 1 one end on the valve and atmosphere intercommunication, the other end are connected with the one end that the filler of nuclear power plant gate valve swept hole and manometer respectively, the other end and the one end of valve 2 of manometer are connected, the other end of valve 2 with suppress a delivery outlet and be connected. Two factories of center operation use in nearly several times overhauls the utility model discloses an it is respond well that the instrument has carried out seal tightness test to a return circuit pressure boundary gate valve.