A two-dimensional self-consistent fluid model is employed to investigate radio-frequency process parameters on the plasma properties in Ar microdischarges.The neutral gas density and temperature balance equations are taken into account.We mainly investigate the effect of the electrode gap on the spatial distribution of the electron density and electron temperature profiles,due to a mode transition from the γ regime (secondary electrons emission is responsible for the significant ionization) to the α regime (sheath oscillations and bulk electrons are responsible for sustaining discharge) induced by a sudden decrease of electron density and electron temperature.The pressure,radio-frequency sources frequency and voltage effects on the electron density are also elaborately investigated.