Ion species ratios in a hydrogen plasma are calculated systematically as a function of plasma parameters, i.e. the electron density, the electron temperature. the pressure of hydrogen gas and the plasma volume. Furthermore, in the present analysis. the recombination factor for hydrogen atoms at thewall surface of a vacuum vessel is treated as another plasma parameter.The most significant point is that ion species ratios depend strongly not only on plasma parameters but also on the recombination factor. The proton ratio increases with decreasing the value of the recombination factor. Primary electrons also play an important role for ion species ratios, and the presence of primary electrons causes the proton ratio to decrease.