A voltage and current control method for DC transmission system, the DC transmission system comprising at least one DC pole, the DC pole having a DC current control end and a DC voltage control end, and the DC voltage control end of the DC pole comprising at least one voltage source converter, the control method comprising: obtaining a DC voltage reference value U dcref required for controlling the DC voltage of the DC voltage control end according to a DC voltage control target of the DC pole, and obtaining a DC voltage measurement value U dV of the voltage source converter of the DC voltage control end; obtaining a DC current reference value I dcref and a DC current measurement value I dc of the DC voltage control end of the DC pole; determining whether the DC voltage control end of the DC pole controls the DC voltage; using the DC voltage reference value U dcref required for controlling the DC voltage as the DC voltage reference value U dVref of the voltage source converter if the DC voltage control end of the DC pole controls the DC voltage; calculating a difference between the DC current measurement value I dc and the DC current reference value I dcref if the DC voltage control end of the DC pole does not control the DC voltage but controls the DC current, and then inputting the difference into the DC current controller of the voltage source converter to perform closed-loop control, and using the output of the DC current controller as the DC voltage reference value U dVref of the voltage source converter; using 1/2 of the DC voltage reference value U dVref of the voltage source converter as a DC bias of the bridge arm voltage of the voltage source converter, and calculating a difference between the DC voltage reference value U dVref of the voltage source converter and the DC voltage measurement value U dv, then inputting the difference into the DC voltage control outer loop of the voltage source converter to perform closed-loop control and realize the control of DC voltage or DC current of the DC pole. obtaining a DC voltage reference value U dcref required for controlling the DC voltage of the DC voltage control end according to a DC voltage control target of the DC pole, and obtaining a DC voltage measurement value U dV of the voltage source converter of the DC voltage control end; obtaining a DC current reference value I dcref and a DC current measurement value I dc of the DC voltage control end of the DC pole; determining whether the DC voltage control end of the DC pole controls the DC voltage; using the DC voltage reference value U dcref required for controlling the DC voltage as the DC voltage reference value U dVref of the voltage source converter if the DC voltage control end of the DC pole controls the DC voltage; calculating a difference between the DC current measurement value I dc and the DC current reference value I dcref if the DC voltage control end of the DC pole does not control the DC voltage but controls the DC current, and then inputting the difference into the DC current controller of the voltage source converter to perform closed-loop control, and using the output of the DC current controller as the DC voltage reference value U dVref of the voltage source converter; using 1/2 of the DC voltage reference value U dVref of the voltage source converter as a DC bias of the bridge arm voltage of the voltage source converter, and calculating a difference between the DC voltage reference value U dVref of the voltage source converter and the DC voltage measurement value U dv, then inputting the difference into the DC voltage control outer loop of the voltage source converter to perform closed-loop control and realize the control of DC voltage or DC current of the DC pole.