In order to control the interference of power current of transmission line on human body, equipment and communication systems in converter station, the magnetic intensity in maintenance hall should be calculated, and the magnetic shielding should be designed according to the requirements. The general formula of magnetic field intensity in valve hall is derived from space coordinates vector formula. Then the magnetic shielding of maintenance hall is designed according to the requirements. Finally, HFSS software is used to verify the correctness of the calculation method of magnetic shielding. The results show that 5 mm aluminum plate is better for the hall sidewall, when the shielding effectiveness in maintenance hall is demanded to be 40 dB, and copper mesh with side length of 20 mm and mesh wire diameter of 5 mm should be laid on ground.