A direct current power grid voltage control method, wherein converter stations in the direct current power grid are divided into three types: power regulation converter stations, auxiliary voltage regulation converter stations, and voltage regulation converter stations, on the basis of whether the converter station has a voltage regulation capacity; the power regulation converter stations operating in a fixed power control mode, the auxiliary voltage regulation converter stations operating in an auxiliary voltage control mode, and the voltage regulation converter stations operating in a fixed voltage control mode or the auxiliary voltage control mode; wherein control of a direct current power grid voltage is divided into three processes being a natural voltage regulation in which a capacitor energy storage in the converter stations in the direct current power grid is used to adjust a direct current voltage in the direct current power grid, a first voltage regulation in which the converter stations operating in the auxiliary voltage control mode are used to adjust the direct current voltage in the direct current power grid, to enable the direct current voltage to form deviation, and the first voltage regulation is completed depending on a controller of a converter station and a second voltage regulation in which the converter stations operating in the fixed voltage control mode or the converter stations operating in the voltage auxiliary control mode are used to adjust the direct current voltage in the direct current power grid, to implement accurate control of the direct current voltage, wherein a controller of the second voltage regulation is mounted inside a converter station or at an external regulation department; all the converter stations in the direct current power grid participate in natural voltage regulation, the auxiliary voltage regulation converter stations and the voltage regulation converter stations participate in first voltage regulation, and the voltage regulation converter stations participate in second voltage regulation; wherein during the regulation the voltage regulation converter stations are switched between the fixed voltage control mode and the auxiliary voltage control mode; characterized in that an implementation method of the auxiliary voltage control mode is: detecting direct current voltage U dc; calculating deviation ΔU=U dc -U rate between the direct current voltage U dc and rated direct current voltage U rate; setting two different fixed voltage deviation values U setH and U setL, U setH >U setL, and comparing ΔU with U setH and U setL, wherein when U setL <ΔU<U setH, ΔU mod =0, when ΔU>U setH, ΔU mod =ΔU-U SetH, and when ΔU<U setL, ΔU mod =ΔU-U setL; calculating a power instruction deviation value ΔP=K ∗ ΔU mod, wherein K is a proportional coefficient; and calculating a power instruction Pref=Porder-ΔP of a power controller according to a power instruction Porder delivered by an upper-layer controller and the power instruction deviation value ΔP. detecting direct current voltage U dc; calculating deviation ΔU=U dc -U rate between the direct current voltage U dc and rated direct current voltage U rate; setting two different fixed voltage deviation values U setH and U setL, U setH >U setL, and comparing ΔU with U setH and U setL, wherein when U setL <ΔU<U setH, ΔU mod =0, when ΔU>U setH, ΔU mod =ΔU-U SetH, and when ΔU<U setL, ΔU mod =ΔU-U setL; calculating a power instruction deviation value ΔP=K ∗ ΔU mod, wherein K is a proportional coefficient; and calculating a power instruction Pref=Porder-ΔP of a power controller according to a power instruction Porder delivered by an upper-layer controller and the power instruction deviation value ΔP.