The invention discloses an estimation method of the beam length of a 500V power transmission line tower pole grounding body. The estimation method comprises the following steps: establishing a tower pole grounding body model; according to the model, calculating the impulse grounding resistance of the tower pole grounding body model; carrying out fitting calculation on the formula of the impulse grounding resistance of the tower pole grounding body; according to the formula of the impulse grounding resistance, fitting the effective length formula of tower pole grounding body ray; and according to practical soil electrical resistivity, obtaining the effective length of the tower pole grounding body ray, wherein the grounding body model comprises four steel bodies and the tower pole grounding body ray arranged on the steel bodies, a square of which the side length is 18m is formed by the four steel bodies, and the adjacent tower pole grounding body rays are not on the same endpoint. The estimation method of the beam length of the 500V power transmission line tower pole grounding body provides a theoretical basis for the design and the transformation of a power transmission line tower pole grounding device, and is favorable for obtaining an excellent grounding body.