The paper reports a novel method of increasing the fraction of H ion produced by vacuum arc ion sources with metal hydride cathodes, which applies the ionic selectivity of inclined-aperture extraction grid to separate and filter heavy metal ions. Since H ion and Ti ion produced by vacuum arc discharge have great differences in kinetic energy and mass-to-charge ratio, H ions are easy to pass through the inclined-aperture grid, while most of Ti ions are blocked and absorbed by the grid wall. Using a 2D particle-in-cell simulation, the ionic selectivity of inclined-aperture extraction grid is demonstrated. The numerical simulation results show that after ion filtering through the extraction grid, the fraction of H ion is increased from 39% to more than 80%. The increased amplitude of H ion fraction depends on the thickness of the grid.