Abstract: Plasma characteristics of an RF ion source were investigated by emission spectroscopy. The RF ion source, applied in ZF200keV neutron generator, is an orbicular discharge RF ion source coupled with inductance. The spectral line intensities of the first three atomic lines in hydrogen Balmer series in different moment of RF ion source plasma, were measured with calibrated optical multichannel analyzer. Some plasma parameters in relevant time, including electron temperature, hydrogen atom density and hydrogen ion density, were calculated and analyzed using partial local thermodynamic equilibrium theory.