Plasma discharge stability is an important problem in atmosphere-breathing electric propulsion system when maintaining long-term missions at ultra-low earth orbit. This paper designed an inductively coupled plasma source to imitate the ionization section. The effect of inflow rate and Radio Frequency (RF) power on the plasma discharge mode transition is experimentally studied. A discharge mode detection method is proposed, which determines the discharge mode by identifying the morphology of the plasma core. By using the method, the discharge mode transition is quantified and a control model based on the parameter sensitivity is constructed. To verify the method, the spectra are measured and the electron temperature spatial distribution is calculated. And the method has been proven effective. The results show that the inductively coupled discharge contains capacitive components affected by the mass flow rate and the radio frequency power. The plasma characteristics can be maintained stably by controlling the radio frequency power when the mass flow rate randomly changes in a certain range. It is demonstrated that the application of detection method effectively identifies the discharge mode, which is a promising active control method for the plasma discharge mode.