The stability of the DC transmission system is of great significance to the safe operation of regional large power grids and the reliability of power supply. With the commissioning of the ± 500kV Lu-Gao-Zhao three-terminal conventional DC transmission project, the power grids of Yunnan, Guizhou, and Guangdong provinces have become increasingly close. The failure of one station will have an impact on the power grids of the three provinces. This paper analyzes the response of the DC system when the AC system on the rectifier side fails, and analyzes the impact on the DC system when the AC single-phase grounding fault occurs on the rectifier side in engineering practice. It is found that when only AC single-phase fault occurs at Luquan Station, It will also have a greater impact on the DC transmission system, and at the same time, according to the analysis, corresponding improvement and pre-control measures are proposed.