Abstract: The paper studied the conversion law of E mode to H mode in inductively coupled plasma (ICP) discharge device in a cylindrical discharge device, by changing the gas flow rate, discharge pressure and gas composition. An emission spectrum diagnosis method was adopted, and the 419.8 nm argon atomic spectrum and 434.8 nm argon ion spectrum were collected and analyzed to characterize the transition power of E to H mode. Results show that when the discharge pressure is 60 Pa, the transition power E-H is minimum; adding He in Ar does not affect the E-H transition power, and after adding N₂, the E-H transition power has changed obviously. With the increase of the argon flow rate, the E-H transition power decreases. The conversion of E mode to H mode is a sudden change process in radio frequency inductively coupled plasma discharge. The transition power varies with different gas flow rates, discharge pressures and gas compositions.