Abstract: In millimeter wave klystron, the electron optics system is very important. The electron optics system is related to the realization and the life time of the klystron. The size of millimeter wave klystron is small. To achieve kW output power in Ka-band and W-band, the higher electron passing rate and lower cathode load are required. The paper analyzes the characteristics of electron optics system for Ka-band and W-band klystron. The design schemes of Ka-band 10 kW klystron and W- band 1 kW klystron are determined. The structures of electron gun and focusing system are calculated by software, and the state of electron gun in focusing magnetic field is optimized by CST. Ka-band klystron and W-band klystron have been made, and the electron optical system designed can meet the requirement of engineering realization of klystron.