We aimed to improve the calculation accuracy by focusing on the neutral radical Ar * and electron density in a dual-frequency excited Ar plasma. The neutral radical Ar * has a long lifetime and becomes exhausted without actually disappearing. The coupled calculation of plasma and gas flow simulation was performed, and confirmed that Ar * in the coupled calculation spreads around, which was not shown by plasma simulation only. Regarding electron density, the effect of the secondary electron emission (SEE) factor was evaluated on basis of the measured electron density. The errors of electron densities between the experimental and simulation results were decreased from 36% to 17% by adding the effect of secondary electrons from the electrodes to the plasma simulation. It was shown that the coupled calculation and the addition of SEE are effective for calculating the dual-frequency excited Ar plasma.