Three poly(ether-b-amide) (Pebax) membranes with different polyamide (PA) contents were prepared to study CH4/N2 gas separation property. The increase in CH4 and N2 gas permeability was observed with the lowering of PA content. It was attributed to the decreased fraction of impermeable crystalline PA regions and the decrease in the crystallinity of the semi-crystalline PA phase of Pebax membranes. This result is consistent with the previous reports on other gases for Pebax membranes. To lower the crystallinity and higher the CH4 permeability, 10 wt% poly(styrene-b-butadiene-b-styrene) (SBS) block copolymer was blended with Pebax. For single gas permeation test, we demonstrated that CH4 permeability of the Pebax/SBS blend membrane is 60% higher than that of Pebax, reaching 106 Barrer at 55 °C. In CH4 and N2 mixed gas permeation test, up to 26 vol% of CH4 could be obtained from passing 10 vol% CH4 of CH4/N2 mixed gas through the Pebax/SBS membranes, demonstrating that Pebax based membranes could potentially be applied to the enrichment of CH4 for the coal-bed methane (CBM).