Porous graphene membranes have been shown to have great selectivity for H2 / H2S separation using molecular dynamics simulations (MD). We designed a series of porous graphene as the separation membrane for hydrogen gas. The permeation process of different gas molecules (H2 and H2S) in porous graphene under constant pressure conditions was investigated. Our results indicate the hydrogen permeability and selectivity could be tuned by the size and the shape of the porous graphene. For graphene with larger pores, the selectivity of hydrogen gas may be reduced.In the porous graphene with same pore area, the hydrogen gas selectivity could be affected by the shape of the pore. Our studies show that the first principles of simulation can be well used to understand MD results and be suggested as an economical and efficient means of separating H2 from H2 / H2S, which may be useful for designing new concept membranes for gas separation.