Perfect station auxiliary power system main diagram and efficient standby power supply automatic switching-on logic should be designed in converter station of HVDC system for the safe and stable operation. According to the electric diagram and operation requirement of Pu'er converter station, five operation conditions are considered and charge/discharge logic and thirteen automatic switching-on/off logic are designed for 10 kV standby power supply automatic switching-on relay, two automatic switching-on/off logics are designed for 400 V standby power supply automatic switching-on relay. Meanwhile, the setting principle and coordination are discussed and the recommended settings are given. The standby power supply automatic switching-on/off logic has been applied in Pu'er converter station, experimental results and operation conditions show that standby power supply automatic switching-on relay will trip the circuit breaker of fault line and switch to standby power supply rapidly while one or two station auxiliary power supply fault without reducing HVDC transmission power, the reliability and stability of HVDC system are greatly improved.