Abstract: This paper demonstrates a sheet beam electron gun designed for high power klystrons to produce the rectangular cross-section beam. The electric parameters are as following: the voltage 300kV, the current 330A, the beam perveance ~2.0, the cathode cross section size 100mm×40mm. Through the single direction compression, the beam size becomes 100mm×8mm, and the laminarity is well satisfied. According to the simulated electric structure, the sheet beam sealed tube has been built and tested. The preliminary experimental results exhibites attained the initial requirement.