Abstract: HVDC technology is an important carrier for the large-scale new energy transmission. In the future, large-scale new energy bases in deserts, and Gobis of China will locate at high altitude which even exceeding 4 000 m. The high flux of cosmic rays and atmospheric neutrons will seriously threaten the safe and reliable operation of power devices in voltage sourced converter-high voltage direct current (VSC-HVDC) valve. However, there are currently no application cases of converter valves in VSC-HVDC projects in China at high altitudes above 2 000 m. Furthermore, there is also a lack of failure rate data of power devices under atmospheric neutron irradiation around the world. The influence of atmospheric neutrons on power devices is unclear, making it difficult to support engineering applications. This article proposes an equivalent accelerated test method for high-altitude atmospheric neutron irradiation effects of power devices such as IGBT and thyristors for 4.5 kV mainstream power devices used in VSC-HVDC. The failure rules of the power devices are studied. And the effects of operating voltage, operating temperature, and neutron flux on device failure rates were analyzed based on the test results. The atmospheric neutron irradiation failure rates of IGBT and bypass breakdown thyristors in high altitude areas are obtained to provide guidance for the safety design of high-altitude VSC-HVDC valves.