At present, the existing fault information management master station or secondary equipment for on-line monitoring and analysis in China only has the ability to monitor and analyze the operation of AC secondary equipment (protection and wave recording device). It does not have the ability to monitor and diagnose the secondary equipment of HVDC. Therefore, a set of monitoring and fault diagnosis master station systems for HVDC secondary equipment is designed and developed. The software and hardware structure of the system, modeling of HVDC secondary equipment and implementation scheme of the main function modules are introduced in detail. Field operation shows that the master station system can quickly and accurately determine the DC protection action and DC fault in the case of faults and abnormal operation in the operation of a DC transmission system, and timely push the relevant fault information to the superior dispatching center. This work is supported by the Science and Technology Project of the Headquarters of State Grid Corporation of China (No. 521104170012) and the Science and Technology Project of State Grid Zhejiang Electric Power Co., Ltd. (No. 5211JX1400LB and No. 5211WZ15013Q).