Abstract: Cylindrical and conical discharge reactors were used for hydrogen discharge at different radio frequency powers. Using mass spectrometry and Langmuir probe, the ion composition, the ion energy distribution (IED), the plasma potential, the electron density and the effective electron temperature were investigated in both the discharge reactors. Based on plasma diagnostic result, the discharge property was discussed in both conical and cylindrical discharge reactors. The results show that there are more H⁺ in conical discharge reactor, but more H^* in cylindrical discharge reactor. In addition, it is shown that the electron and ion densities are higher and the plasma potential is lower in conical discharge reactor.