The　key　to　preparing　dense　composite　membranes　is　reducing　the　thickness　of　the　composite　layer　with　stable　separation　performance.　Herein,　we　report　a　nanoconfined　composite　membrane　prepared　by　in　situ　growth,of　Zeolitic　Imidazolate　Framework　(ZIF)　nanocrystals　in　the　nanoporous　layer　of　the　substrate　via　a　fine-tuning　contra-diffusion　method.　The　thickness　of　the　composite　layer　on　the　membrane　surface　was　nearly　zero.　The　formed　ZIF　nanoconfined　composite　membranes　showed　state-of-art　flux　and　high　stability　in　removing　dyes　from　water.　This　new　strategy　is　expected　to　offer　great　opportunities　for　the　potential　practical　application　of　polymer-supported　metal　organic　framework　(MOP)　composite　membranes.