When the electric field intensity under the high voltage AC power transmission line exceeds the standard limit, a grounded metal shielding net is usually used to reduce the electric field intensity. The paper studies the calculation method of the shielding effectiveness of the finite size metal shielding net, this method of the shielding net’s shielding effectiveness is more in line with the requirements of the actual scene. On this basis, the influence laws of different shielding net layouts, shielding conductor density and shielding conductor thickness on the shielding effectiveness are obtained. The results show that the most important factor affecting the shielding effectiveness of finite size shielding net is the density of the shielding net. The layout and the thickness of the shielding conductor have little effect on the shielding effectiveness of the shielding net. The results can provide technical support for the layout and design of the shielding net.