The magnetic field distributions and photoelectron trajectories of the camera are simulated, the two-dimensional distribution model of the transmission time and distance are built, and the causes and reduction methods for the magnetic focusing temporal dispersion and distortion are analyzed. The research results show that, the temporal dispersion and distortion are closely related to the magnetic field intensity along the axis of object point (cathode position), which increase with the increase of the off-axis distance of object point indicating that the magnetic focusing temporal dispersion and distortion can be reduced by the improvement of the uniformity of the axisymmetric magnetic field. As the gap of the magnetic leakage broadens from 4 mm to 40 mm, the peak value ratio between the on-axis magnetic field intensity and the 30 mm off-axis one increases from 0.82 to 0.89. Simultaneously, the temporal dispersion is reduced from 127 fs and 435 fs to 120.6 fs and 378.4 fs, respectively, and the temporal distortion for 30 mm off-axis decreases from 4.61% to 4.01%.