In this paper, a glass tube closed plasma chamber is designed. The high-frequency switching power supply is used as the working power source and the high purity argon gas (99.999%) is used as the working gas. The relationship between plasma density and current is deduced based on the theory of Townsend discharge, and the theory is validated by the experimental results, and tested the different pressure, different electrodes under the closed plasma density. The experimental results show that the closed plasma density can be increased to 1.1 × 10₁₃cm_-3 under the condition that the pure hot metal cathode material is used as the electrode, the working current is 200mA and the tube pressure is 0.5torr. The relationship between the density of the closed plasma and the current, the gas pressure in the chamber and the chamber electrode is analyzed, and a method of obtaining the high density plasma close to the arc discharge in the closed cavity is explored.