At present, the simulation research of arc actuators is limited to only obtaining the working characteristics of the plasma generated by the actuator, such as potential, pressure, temperature and velocity, while the plasma state is limited to only diagnosing its electron temperature and electron density by spectrum. The two are separated. This paper attempts to unify the two. Therefore, the arc jet plasma actuator designed here adopts the finite element method to solve the nonlinear multi physical equations. The working characteristics of the arc jet plasma actuator are numerically simulated, and the potential, pressure, temperature and velocity distributions inside the actuator are obtained. On this basis, the electron density is calculated and the simulation calculation model of the plasma state (electron temperature and electron density) of the actuator is obtained from the working condition of the actuator. Then the spectral diagnosis of the jet plasma is carried out by using the emission spectral diagnosis method, and the electron density of plasma is calculated by using the intensity ratio method of discrete spectral lines. The diagnostic experiment of the arc plasma actuator shows that the maximum electron temperature is 10505.8 K and the maximum electron density is 5.75×10²² m^-3. For the plasma electron temperature and plasma density under different working conditions, the experimental and simulation results increase with the increase of inlet gas flow and discharge current. It shows that our simulation model of plasma state is reasonable and applicable for our miniaturized arc jet actuator with high jet velocity.