The mode transition and coexistence were investigated in atmospheric pressure argon radio frequency capacitive discharge. By use of a program compiled by the authors for the nitrogen's second positive band simulation, comparison between the experimental and simulated spectra of band (0, 1) and (1, 2) was used to determine the rotational and vibrational temperatures of N2. The trends of vibrational and rotational temperatures with discharge power were studied to observe the temperature jump corresponding to the discharge mode transition. Utilizing a well-known software named Lifbase, the simulated spectra of OH (A—X)(0, 0) was calculated to obtain the rotational temperature of OH by comparing with the experimental OH (A—X)(0, 0) band. The calculated rotational temperature of OH is well consistent with the result of nitrogen's second positive band, which shows that the neutral species are at thermal equilibrium in the space of discharge. According to the current-voltage characteristic, the temperature jump corresponding to the discharge mode transition was confirmed in accordance with the photograph of discharge.