The transient overvoltage of converter side AC bus caused by DC block may influence the stable operation of wind-thermal-bundled AC system wind turbines. To solve this problem, this paper firstly analyzes the main reasons of transient overvoltage caused by DC block and its impact on wind turbines. Then dynamic overvoltage caused by DC block and protection operating process are expounded. Besides, the HVDC system model called Cigre_Benchmark in PSCAD is modified, and the modified model is used to simulate and analyze the trigger mode of DC block and the process mechanism of transient overvoltage. The emergency switch off sequence strategy triggering DC block is improved, the triggering process of DC block is retarded, and the trigger sequence of protection measures is changed. And the former strategy works with safety control system to suppress transient overvoltage of the grid-connected bus of converter side, by which the steady operation of wind turbines is guaranteed. The wind-thermal-bundled HVDC model is built based on PSCAD/EMTDC. Finally the effectiveness of the method mentioned is proved by example simulation. This method has certain value for the study of voltage stability of wind-thermal-bundled HVDC system.