In the power system， high voltage direct current transmission （HVDC） system has the advantages of low cost， low loss， and flexible power flow control. The article provides a detailed introduction to the composition， working principle， and specific application issues of HVDC systems. A simulation model was established and the impact of grounding short circuit and disconnection faults on the system was analyzed. The simulation results show that the system can achieve self recovery through constant voltage and current control after transient faults， but its stability is weak in millisecond level faults， which may lead to instability. The research in this article provides a certain reference for the reliability of HVDC systems in practical applications.