Abstract: Hydropower and new energy in Northwest China are bundled and sent out through line-commutated converter HVDC (LCC-HVDC) transmission system. When the monopole blocking fault occurs in LCC-HVDC, the sending end system will bear severe overvoltage impact. Due to the leading phase operation ability of the sending end hydropower unit, its dynamic reactive power capacity can be further explored to restrain the system overvoltage, but the research on the leading phase coordination of hydropower unit is almost blank. In addition, the power angle stability characteristics of the hydropower unit under the leading phase coordination control are not clear, so it is urgent to carry out research. For this reason, firstly, according to different degrees of overvoltage conditions of the sending end system, the leading phase coordination strategy of hydropower units was proposed, including the coordination of hydropower and HVDC converter station, and the coordination between hydropower units. Secondly, based on the analytical expression of electromagnetic power and equal area criterion (EAC), the power angle stability characteristics of hydropower units before and after LCC-HVDC monopole blocking were studied. Then, in order to ensure the power angle stability of the system, the variation law of the maximum leading phase depth of the hydropower unit before and after line-commutated converter hydropower unit before and after LCC-HVDC monopole blocking was analyzed, and an improved method of low excitation limit curve was proposed to adapt to the leading phase coordination strategy. Finally, the verification test was carried out based on the PSCAD/EMTDC model of an actual wind-solar-hydro sending end system in Northwest China. The results show that the leading phase coordination strategy and the improved method of low excitation limit curve proposed in this paper can further improve the overvoltage suppression ability of the sending end system on the premise of ensuring the power angle stability, which has guiding significance for practical engineering.