The invention discloses a device and a method for detecting a subsea valve in a laboratory. The device for detecting the subsea valve is connected with the subsea valve, and comprises an air source, an air source switch, an air source triplet, a three-position four-way manual valve, a water groove, a pressure reducing valve, a two-way manual valve, an air inlet pipeline, an air outlet pipeline, a bottom valve pressure test tool and a pressure test cover; a flange plate at the bending end of the subsea valve is connected with the bottom valve pressure test tool by a sealing pad, the centre of the bottom valve pressure test tool is connected with a first pressure inlet, a flange plate at the cylinder end of the subsea valve is connected with the pressure test cover by a bolt and the sealing pad, and the pressure test cover is connected with a second pressure inlet. The device can detect the tightness of the cylinder of the subsea valve, the tightness and the reverse tightness of the structure of the subsea valve, and has advantages of simple structure, convenient operation, easy observation, reasonable arrangement and convenient maintenance. The pressure reducing valve in the gas circuit can automatically adjust pressure in an air path, prevent the excessive opening pressure of the subsea valve and reduce the impact to the subsea valve.