Mixed matrix membranes (MMMs) are challenged by the non-ideal interfacial morphologies that leads to the weakened gas separation performances and mechanical strength. Filler surface modification with organosilanes is an effective approach to build the linkage between polymer and the fillers. In this study, we fabricated MMMs by introducing aminosilane functionalized graphene oxide (f-GO) nanosheets into Pebax (R) 1657 matrix. The introduction of f-GO decreased the crystallinity and increased chain mobility of Pebax matrix. Benefiting from the improved filler dispersion, semi-interpenetrated Pebax chains in the Si-O-Si network at the interface, and the high intrinsic mechanical strength of GO, the MMMs exhibit a 1.7-times higher Young's modulus and 1.1-times higher break strength. The amino groups on GO help to construct a facilitated transport pathway along the polymer-filler interface. With greatly improved CO2 separation performances in dry state, the membranes exhibited even higher performances in humidified state. Particularly, Pebax/f-GO-0.9% membrane showed a high CO2 permeability of 934.3 Barrer, and a CO2/CH4 selectivity of 40.9, a CO2/N-2 selectivity of 71.1, surpassing the Robeson upper bound and quite promising for carbon capture.