The utility model belongs to the technical field of nuclear power plant instrument pressure control, and particularly relates to a nuclear power plant welding check valve sealing test device. The device comprises a metal hose A, a locking flange A, a locking flange B, a metal hose B, a test bed and a water tank, wherein the lifting check valve is fixed on the test bed through a locking flange A and a locking flange B in a butt clamping manner, and the metal hose A and the metal hose B are respectively connected with the locking flange A and the locking flange B; the metal hose B extends into the water tank; the metal hose A is connected with an air source. The device can test whether the welding check valve leaks or not, if the welding check valve leaks or not and the leakage rate meets the design requirement range or not, testing is conducted after grinding is conducted if the welding check valve leaks or not and the leakage rate is not within the range. Before the tool is invented, due to the fact that the leakage rate cannot be measured, if the check valve has the oil leakage defect, only the whole valve can be replaced; at present, the availability of the check valve can be judged according to the leakage condition, if the leakage rate meets the requirement, the whole valve does not need to be replaced, and production cost is saved.