In this study, we use the density functional theory (DFT) calculations and the molecular dynamics (MD) simulations to investigate the performance of graphenylene-1 membrane for hydrogen (H 2 ) purification and helium (He) separation. The stability of this membrane is confirmed by calculating its cohesive energy. Our results show that a surmountable energy barrier for H 2 (0.384 eV) and He (0.178 eV) molecules passing through graphenylene-1 membrane. At room temperature, the selectivity of H 2 /CO 2 , H 2 /N 2 , H 2 /CO and H 2 /CH 4 are obtained as 3 × 10 27 , 2 × 10 18 , 1 × 10 17 and 6 × 10 46 , respectively. Furthermore, we demonstrate that graphenylene-1 membrane exhibits the permeance of H 2 and He molecules are much higher than the value of them in the current industrial applications specially at temperatures above 300 K and 150 K, respectively. We further performed MD simulations to confirm the results of DFT calculations. All these results show that graphenylene-1 monolayer membrane is an excellent candidate for H 2 purification and He separation. arXiv:1909.02112v2 [cond-mat.mtrl-sci]