The invention discloses a method for evaluating the influence of DC magnetic bias on a grounding grid of an electricity system. The method comprises the following steps: determining a grounding electrode, a power transmission line and pole towers, acquiring the parameters of the power transmission line in a circle and the parameters of the pole towers in the power transmission line, simulating in an electromagnetic field-circuit coupling manner according to the parameters and the information of the grounding electrode in combination with a moment method and a finite element method, obtaining the current value of each pole tower on a down lead, and then determining whether the current value exceeds the standard or not through judging whether the current value exceeds a standard electrochemical corrosion current threshold or not. The method for evaluating the influence of the DC magnetic bias on the grounding grid of the electricity system, provided by the invention, is simple in calculation, high in accuracy and efficiency and feasible. The method improves the reliability of the grounding system, reduces the lightning trip-out rate of the electricity system and improves the running stability of the whole electricity system.