In this paper, a closed plasma generator is designed. The discharge experiments are carried out in the closed cavity under low pressure environment by adopting the method of inductively coupled plasma(ICP) and taking argon as a working gas. The distribution rules of the electron excitation temperature, electron density, and the effect of RF power on the electron excitation temperature and electron density are investigated by means of emission spectrum. The changes in the electron excitation temperature are analyzed by using the method of the Boltzmann plot, and the variations in the electron density are derived from the analysis of Ar 750.38 nm line intensity. A uniform plasma sheet is produced stably by the closed plasma generator, in which the electron excitation temperature is about 9 500 K. The electron density and electro excitation temperature can be enhanced by improving RF power. With adequate input power, the variations of parameters of the closed plasma at different positions change little.