Three aromatic polyamides (PA) were synthesized from 2, 6-bis (4-aminophenyl)-4-(3-(1,1,2, 2-tetrafluoroethoxy) phenyl) pyridine and commercial diacid. The chemical structures of diamine monomer and polymer were confirmed by FT-IR and NMR. The prepared PAs have good organic solubility, completely soluble in NMP, DMF, DMSO and other high boiling point organic solvents at room temperature, and partially dissolved in THF, CHCl3 and other low boiling point organic solvents at heating state; the glass transition temperature (Tg) is higher than 217 °C, 10% mass loss temperature in N2 is above 512 °C; the cut-off wavelength (λcut-off) and wavelength of 80% transmittance (λ80%) are in the range of 376 ~ 391 nm and 449 ~ 481 nm, respectively. The free volume fractions of PAs were calculated by molecular dynamics simulation, which clarify that the introduction of large side groups and asymmetric structure into the polymer effectively suppress the close packing of molecular chains and form the gas transport path. The PA films were measured for He, CO2, O2, N2 pure gas permeability, three films show relatively similar gas permeability. Compared with PA-1 and PA-2, PA-3 has the best gas separation performance, showing relatively high P(He) = 11.27 barrer, low P(N2) = 0.3294 barrer gas permeability, which makes the He/N2 selectivity of PA-3 improved, i.e. α(He/N2) = 34.21.