Abstract: This paper presents a simulation study on intense relative multi-beams(IRMBs) electron explosive emission and structure optimizing of cathodes in the relative klystron amplifier(RKA) diode with PIC simulation software. Three new kinds of structures for multi-beam cathodes are introduced. The result shows that, the traditional structure cathode could only get the injection coefficient of IRMBs up to 82%, while the new structure cathode could increase it to more than 95%, even 99%. This research gives a solution to the problem of low injection coefficient in the multi-beams RKA.