The HVDC converter valve is an important equipment to realize power transmission under high-voltage direct-current condition. The reliability of high-voltage direct current (HVDC) converter valve directly affects the operation of HVDC converter valve. At first, the typical situations inside the converter valve over-voltage are analyzed and summarized in this article, and then analyzes the broadband model of each component in the converter valve, and establishes the broadband model of the valve tower based on this. Then this paper analyzes the over-voltage distribution of the converter valve under several fault conditions through model simulation, such as HEMP, operating over-voltage and lightning over-voltage. Through the summary of several over-voltage distributions, the over-voltage mechanism of HVDC converter valve is more deeply understood and the theoretical guidance for improving the reliability of the HVDC converter valve during high-voltage power transmission is provided.