Abstract: In the process of depositing polycrystalline diamond thin films by microwave plasma method, the adjustment of process parameters often has a greater impact on the size and uniformity of the plasma ball. Based on the 5 kW MPCVD cylindrical chamber made in the laboratory, this paper combines multiple physical fields to study the axial and radial electron density distribution on the surface of tungsten plate under hydrogen discharge conditions under different process parameter conditions, and evaluates the uniformity of the plasma distribution using the coefficient of variation. The main process parameters include input characteristics (power and pressure), different heights of tungsten plates, and the use of different height tungsten rings. The simulation results show that the volume of the plasma ball increases with the increase of power and decreases with the increase of pressure. Compared with power, pressure change has a greater impact on the axial uniformity of the plasma ball electron density. The surface radial uniformity of the tungsten plate will be affected by the height being too low or too high, and the more obvious edge discharge phenomenon will be observed as the height increases. The addition of tungsten rings can improve the surface uniformity, and the radial uniformity is better when the height of the tungsten plate and the tungsten ring is approximately the same, among which the coefficient of variation of the radial uniformity is 11.1% when the tungsten plate is 0.2 mm higher than the tungsten ring, an improvement of 59.6% compared with the condition without tungsten ring.