Taking the ± 500 kV Deyang Converter Station as an example, the main pump shaft seal water seepage and the scaling of voltage sharing electrodes are two typical hidden troubles which may cause HVDC equipment outage. Through the defects treatment of shaft seals for many times, tracking and analysis continuously in the operation process of equipment, it can be basically determined that cavitation vibration is the reason which causes shaft seal water seepage. In order to prevent and control this hidden trouble, three improving suggestions are put forward, including motor selection, motor controlling and improving the main pump outlet pipe road, and then the improvement program is determined as adding the bypass in the main pump outlet pipe road for its economy and stability. Electrode scaling and corrosion is checked to determine the influence of HVDC transmission system caused by electrode scaling, the cause of the electrode scaling is determined according to the analysis of the constituents content in scaling electrode, and then the electrodes are descaled. The hidden trouble of radiator corrosion caused by water quality is solved by changing the cooling water medium, and according to the closed structure of inner cooling water system, an improved scheme by adding gasbag is designed to descale the electrodes. Analysis and governance of the two hidden troubles will provide the guidance for selecting and designing of related equipment in new converter, and provide a reference to analyze the similar hidden hazard for completed converters.