Low-pressure discharge is an important problem that restricts the development of microwave components of spacecraft toward high-power and miniaturization. To clarify the mechanism of low-pressure discharge of microwave component in spacecraft, we build an emission spectroscopy diagnostic platform for studying the low-pressure radio frequency (RF) discharge plasma, and investigate the plasma reaction dynamics of low-pressure RF discharge of microwave cavity resonator and the damage effect of discharge on microwave component. The emission spectra of the plasma inside the resonator under different gas pressure conditions are obtained, and it is found that the density of hydroxyl OH (A-X), excited nitrogen molecules N₂ (C-B) and oxygen atoms O (3p⁵P→3s⁵S⁰) in the plasma each show a first-increasing and then decreasing trend with the increase of gas pressure. The kinetic mechanism of the plasma reaction behind this phenomenon is analyzed, and it is found that the gas pressure can influence the concentration magnitude of each species in the plasma by changing the species production and consumption paths as well as the average electron temperature of the plasma. The variation law of plasma emission spectrum with the input power is studied, and the trends of linear increase of particle concentration with the increase of input power at different air pressures are found. This study provides a reference for investigating the mechanism of low-pressure RF discharge and the reliable design of spacecraft microwave components.