To systematically explore polymer-filler interface and its influence, a series of mixed matrix composite membranes were fabricated by coating the mixture comprised of polyvinylamine(PVAm) and different inorganic nanofillers on polysulfone(PS) flat ultrafiltration membranes. Multiwalled carbontube (MWCNT), SiO2 and ZSM-5 were chosen as pristine inorganic nanofillers, and MWCNT-NH2, SiO2-NH2 and ZSM-5-NH2 were used as modified inorganic nanofillers. Possible gas transport mechanisms are discussed. A method of assessing the size of interface voids is developed by analyzing a trend in gas permeance with increasing feed pressure. The effect of feed pressure on gas permeance of the mixed matrix composite membranes was investigated. For PVAm-pristine inorganic nanofiller/PS membranes, membrane compaction, void-filling effect, surface flow and interface void channels affect its N-2, O-2 or CH4 permeance change with increasing feed pressure. The size of interface voids varies in the order of PVAm-ZSM-5 interface voids >PVAm-MWCNT interface voids >PVAm-SiO2 interface voids. Furthermore, gas permeance of PVAm-modified inorganic nanofiller/PS membrane is lower than that of the corresponding PVAm-pristine nanofiller/PS membrane. The result suggests that surface modification of inorganic nanofillers with compound containing the same functional groups as polymer is an effective way to improve the interface compatibility between polymer chains and modified inorganic nanofillers. (C) 2015 Elsevier B.V. All rights reserved.