A method of combiningthe fluid model simulation and the emission spectrum was used to study the discharge characteristics of Radio-frequency (RF) capacitive coupled plasma in medium pressure and medium power. In theory, one-dimensional discharged plasma model is taken using COMSOL software based on the fluid model. The distributions of electron temperature and electron density of plasma were studied under different air pressures and different radio-frequency powers with the Ar gas as the working gas. In experiment, a glass sealed cavity and a pair of plate electrodeswere designed and fabricated with the same sizes of the simulation model. Using 13.56 MHz radio frequency discharge technology to ionize the working gas of Ar gas in the cavity. The emission spectra of discharge plasma at different pressures and different RF input powers were measured. Through the analysis and selection of suitable spectral lines of ArⅠ and ArⅡ, the electron temperature and electron density of the plasma were calculated by the Boltzmann method and the Shah-Boltzmann equation, respectively. And then these results of spectral diagnosis were modified by combining with simulation results. The results show that when the gas pressure is 300~400 Pa and the radio-frequency power is 600~800 W, the plasma satisfy the Boltzmann distribution approximately. The plasma parameters obtained by the spectroscopic method are in agreement with the simulation results. The discharge parameters of the plasma under the medium pressure can be diagnosed by the method of combing the fluid model simulation and the emission spectrum, which provides a reference for the following study about the plasma properties. The method combining the fluid model simulation and the experimental spectrum diagnosis can be used to diagnose the plasma discharge parameters at medium pressure and medium power, which increases the range of use in plasma discharge in the Boltzmann slope method and the Saha-Boltzmann equation, and expands the application of spectroscopy in low electron density capacitive coupled plasma diagnostics. Also it provides an important physical state analysis for the study of medium pressure capacitive coupled plasma in industrial and military applications.