The reliable transmission of the HVDC pole control signal is considered to be the key to make HVDC system run stably. In recent studies, the whole procedure analysis of pole control signal is not mentioned, and the influence of different service demand on pole control signal reliability is ignored. The influences due to pole control signal lost is established, and the transmission process of DC pole control signal between PCM access and router access is compared. Combined with the pole control system reliability demand of different operation mode and risk grade, reliability analysis method based on the signal transmission capacity is proposed. By calculation and analysis of reliability in ± 500 kV Gaozhao DC and ± 800 kV Chusui DC, the trend that reliability varies with the service demands is then evaluated, and then the transmission reliability of pole control signal is compared and analyzed. In the end, the methods to improve the reliability of DC pole control signal transmission are summarized. It has a guiding significance to improve the stability of DC control system.