Nanocomposite membranes incorporating high-aspect-ratio nanostructures within polymeric matrices are highly promising for controllable molecular separation. Zeolitic-imidazolate frameworks (ZIFs) has been extensively investigated as nanofillers or surface coating materials devising innovative membrane design. This work for the first time reports an innovative approach to in-situ form ZIFs within polymeric membrane matrix to regulate the molecular sieving behavior of the thin composite layer. A chelation-assisted interfacial reaction strategy was applied to incorporate vertically-oriented ZIF into the crosslinked poly (vinylamine) (PVAm) matrix. PVAm has a good ability to complex with Zn2+, thus provides a highly concentrated zinc source within the matrix and ensures good adhesion between the ZIFs and substrates. Due to the intimate integration of ZIFs with PVAm, the composite layers have good flexibility and tensile strength. It also leads to the absence of micro-defects within the layer. The membranes exhibited reversed selectivity for the CO2/N-2 gas pair, with N-2/CO2 selectivity of 51.9 and N-2 permeance of 174.9 GPU. The results of this work provide an important technique to regulate the interfacial interaction to regulate the gas separation behavior within the composite membrane.