Abstract: This paper describes physics processes of the discharge within an orificed hollow cathode.On the basis of parameters of the 8-cm mercury ion thruster and hollow cathode,the pressure、particle density、initial energy exchange mean free path of electron within the hollow cathode were calculated.Thus main dimensions of emitter and top orifice of catthode were designed.The emission carrent of cathode was checked.The parameters of heater and thermal-equilibrium of cathode were calculated and comparad with results of experiments.According to operating mode of the cathode in the thruster,the design of the cathode structure,including selection of the materials and the technology of the plasma spray,were described.The re- suits of the long-term thermal-simulation experiments were given.