In this study, we have demonstrated a simple, scalable, and environmentally friendly route for controllable fabrication of continuous, well-intergrown ZIF-8 on a flexible polymer substrate via contra-diffusion method in conjunction with chemical vapor modification of the polymer surface. The combined chemical vapor modification and contra-diffusion method resulted in controlled formation of a thin, defect-free and robust ZIF-8 layer on one side of the support in aqueous solution at room temperature. The ZIF-8 membrane exhibited propylene permeance of 1.50×10-8 mol m-2 s-1 Pa and excellent selective permeation properties; after post heat-treatment, the membrane showed ideal selectivities of C3H6/C3H8 and H2/C3H8 as high as 27.8 and 2259, respectively. The new synthesis approach holds a promise for further development for the fabrication of high-quality polymer-supported ZIF membranes for practical separation applications.