According to the failure statistics and feedback of coal mine users on supporting equipment, when part of the hydraulic valve in the hydraulic system is under low pressure, the frequency of slow leakage is relatively high.In order to adapt to the emergency repair of hydraulic valve and other components in downhole, and to ensure the safety of working face support, a testing equipment with a small volume was designed, which was convenient for ground and downhole handling and installation.The overflow valve in the low pressure sealing performance test circuit was one of the key components. The principle and structure of the existing straight moving relief valve were analyzed, and the valve core, valve seat and valve body were innovatively designed to keep good sealing performance within a certain pressure range.The test results show that the sealing of the relief valve is reliable under the pressure of 2 MPa , it reaches the test standard of the low pressure sealing performance of mine hydraulic components