Abstract: A series of optimization designs of electron diode in 12MeV linear induction accelerator are studied by using numerical simulation code MAGIC and experiment method in order to improve the electron beam quality.MAGIC code solves the Maxwell equations in the presence of charged particle,Electron field distribution on cathode surface which influences electron emission can be given,the optimum diode is obtained by comparing to the results of experiment in 12MeV, then the paper gives SEM analysis and experiment comparison of velvet emission. Finally, emitted current Ie= 8.52kA ,beam current I8= 3.0kA, targeted current I0= 2.30kA with optimum diode are obtained.