First principles based DFT calculations performed to insight structural and electronic properties of Boron doped Magnesium atom decorated graphene sheet for application of hydrogen storage. The four H2 molecules stably binds magnesium atom with Boron doped graphene sheet. The average binding energy extracted in the range-0.566 to -0.687 eV/H2.Partial density of states of complex system shows s and d orbitals of H2 molecule and Mg atom at -0.1eV overlaps of main peaks indicates strong hybridizing and binding of s and d orbitals of H2 and Mg atom respectively. The gravimetric capacity of studied complex system reaching approximately 8.26 wt% hydrogen. HOMO & LUMO study shows stability of complex system.DOS investigation reveals the electronic density of states of complex system.