The variations of the main positive ion components and their energies for the plasma of H2/C4H8 gas mixture under different working pressures are investigated using the glow discharge technique and plasma mass spectrometry diagnostic method, and the effects of work pressure on both the dissociation mechanism of the mixed gas H2/C4H8 and the forming process of the main positive are analyzed. The results show that both the intensity and energy of the C-H segment ions in H2/C4H8 plasma decrease with pressure increasing. The relative concentration of m/e 41(C3H5+) reaches a maximum when work pressure is 5 Pa. And when the pressure is 10 Pa, the relative concentration of m/e 39(C3H3+) is largest; when the pressures are 15 Pa and 20 Pa, the relative concentration of m/e 29 (C2H5+) is highest; when the pressure is 25 Pa, the relative concentration of m/e 57(C4H9+) is biggest. The component and its energy distribution of H2/C4H8 plasma are qualitatively analyzed. The results will serve as a reference to the optimization of parameters for glow plasma polymer coatings.