HVDC pole blocking in AC-DC hybrid power grid may cause serious problem of system security and stability. Hence it is very important issue to correctly detect HVDC pole blocking in the power system stability control. By digital simulation， the influence of HVDC pole blocking on power system stability is analyzed. Results in the paper indicate that the system protection must detect all kinds of pole blocking contingencies correctly and quickly. Based on the electrical characteristics of HVDC pole blocking and the operation of HVDC control system， the reliable HVDC pole blocking universal detection is proposed and explained in detail. Through the introduction of the Gaopo-Zhaoqing HVDC stability control system， which is the core of the stability control system of China Southern AC-DC hybrid power grid， the importance of detecting HVDC pole blocking and corresponding stability control are further explained.