Hydrogen storage capacity on vanadium (V) decorated porous graphene (PG) has been studied using first-principles calculations. The results show, to avoid a tendency of clustering among V atoms, the maximum number of adsorbed V atoms is two for both sides of the PG unit cell, and four H-2 molecules can be adsorbed around each V atom. Furthermore, at 300 K and without external pressure, ab initio molecular-dynamics simulations results show that six H-2 molecules can be stably adsorbed on both sides of unit cell of PG decorated with V atoms with the gravimetric hydrogen storage capacity of 4.58 wt%.