The present invention provides a method for obtaining maximum injection current at a grounding electrode position in a DC transmission system. The method comprises the steps of collecting data information for calculating the maximum injection current at the grounding electrode position; obtaining a maximum DC invasion current value of a transformer; establishing a circuit model of DC distribution of an AC system, and calculating grounding body potential of each substation; establishing a soil resistance network model, and calculating a current value required to be injected to the grounding electrode position when the grounding body potential of each substation rises; and obtaining the maximum injection current at the grounding electrode position in the DC transmission system. According to the method, safe and stable operation of the whole system can be ensured without changing the operation mode of the AC system. In addition, the method can also provide design foundation for design planning, operation mode determination and grounding electrode design mode of an AC-DC hybrid power grid, and provide data support for configuration of DC magnetic bias treatment equipment, evaluation of treatment effects, and design of high-voltage DC transmission control strategies.