Poisson Superfish and General Particle Tracer were used to simulate UED DC photocathode electron guns with different magnetic shielding plates. The smaller the center hole of the magnetic shielding plate, the better the magnetic field shielding. The shielded magnetic field is proportional to the aperture radius. Continuing to reduce the hole does not significantly improve shielding, while the central hole is too small. The thicker the magnetic shielding plate, the better the shielding effect, but the improvement is not significant. The shielded magnetic field is inversely proportional to its thickness.The closer the magnetic shielding to the electron gun, the larger the field in the gun, which mainly due to magnetic leakage from the central hole. The shielded magnetic field is inversely proportional to the distance from the cathode. The installation of magnetic shielding plates leads to premature focusing of electronic pulses and a smaller focusing radius. The smaller the center hole in the magnetic shielding plate, the smaller the focusing radius and focal length. The thicker the magnetic shielding plate, the smaller the focusing radius and focal length. The farther the magnetic shielding plate to the electron gun, the smaller the focusing radius and focal length. The better the magnetic field shielding , the smaller the magnetic field between the electron gun and the magnetic shielding, and the smaller the electron pulse focusing radius and focal length