Abstract: In this paper, we briefly introduce the structure of the LaB₆ thermionic cathode for 1 + 1/2 RF cavity. The heating balance power of thermionic cathode and the emission status of electrons from the high temperature in high RF field have been analyzed.The electron beam current density of LaB₆ versus cathode heating power have been given. Finally,problems of stability of the LaB₆ cathode have been also studied.