The beam shape distortion of the pseudospark pulsed electron beam in transmissi on has been observed by the beam bombardment of the color changeable film and t he single crystal silicon. Based on the beam self-pinch effect, the mechanisms of the beam shape distortion have been analyzed by the theoretical calculation of the radial force of electron beam. The results showed that the elliptic beam shape was caused by the azimuthal magnetic field of transient currents, which past through the parallel charging capacitor, and the method for solving beam shape distortion in transmission was also presented.