Abstract: The design requirements and structural peculiarity as well as performance requirements of the steam safety valves which are nuclear safety class 2 component installed in the over-pressure protection system of the second loop of 10 MW High Temperature Gas-cooled Reactor(HTR-10) are introduced. The demonstration test for full performance of the steam safety valves was carried out in special test system. The test results show that the performance of the steam safety valves can meet the design (requirement) and relevant nuclear code.