Abstract: In order to optimize the feeding way of the propellant into the 20 cm diameter ion thrusters discharge chamber, the fluid velocity and pressure at the interface of the thruster anode and main cathode were studied without discharge process, and then the fluid field inside the discharge chamber was calculated. The results indicate that the pressure at the outlet of the thrusters anode gas feeding component is in the range of 4-158 Pa, the exiting velocity of the gas flow is approximately in the range of 0.1-47 m/s. The pressure at the outlet of the cathode aperture is approximately 33.1 Pa, and the velocity is approximately 12 m/s. considering the backstreaming of the vacuum system, the pressure inside the discharge chamber in the range of 0.001-0.4 Pa, the density distribution of Xe atom is not uniform and in the range of (0.2-3)1018 m-3, the density near grids assembly is about 91019 m-3. With the addition of a number of anode feeding pipes, the exiting velocity of the anode gas feeding component is in the range of 18-40 m/s, and the pressure inside the discharge chamber in the range of 0.03-0.1 Pa. When the density of Xe atoms in most part of the discharge chamber is about (0.72-2.4)1019 m-3, the atom density in a small part near the anode and the main cathodes gas-in end is of the order of 21017 m-3 and the discharge has a relatively overall uniform density distribution.