Abstract: Abstract：Plasma technology is more and more widely used in the semiconductor chip etching process. It is particularly important to study the mechanism and working conditions of plasma discharge.The Langmuir probe diagnostic device was used to measure the electron temperature and the plasma density, and the spectral intensity measured by the emission spectroscopy diagnostic device was used to determine the discharge mode in the experimental chamber. The results show that the plasma discharge can be converted in E mode and H mode, the spectral intensity and plasma density appears inverse hysteresis phenomenon with the change of power. When the working pressure is in the range of 0.36Pa to 0.42Pa, the hysteresis will no longer exist. In addition, as the vacuum chamber pressure increases, the jump power of the E-H mode conversion decreases first and then increases, and is the lowest at a working pressure of 0.39 Pa. The greater the RF power, the greater the range of barometric pressure required for the gas to remain in H-mode. All of these can provide reference for the control of the air pressure in the actual industrial production.