Yolk-shell　nanoreactors　have　received　considerable　interest　for　use　in　catalysis.　However,　the　controlled　synthesis　of　continuous　crystalline　shells　without　imperfections　or　cracks　remains　challenging.　Here,　a　strategy　for　the　synthesis　of　yolk-shell　metal　nanoparticles@covalent　organic　framework　(MNPs@COF)　nanoreactors　by　using　MNPs@ZIF-8　core-shell　nanostructures　as　a　self-template　is　designed　and　developed.　The　COF　shell　is　formed　through　an　amorphous-to-crystalline　transformation　process　of　a　polyimine　shell　in　a　mildly　acidic　solution,　while　the　ZIF-8　is　etched　in　situ,　generating　a　void　space　between　the　MNPs　core　and　the　COF　shell.　With　the　protection　of　the　COF　shell,　multiple　ligand-free　MNPs　are　confined　inside　of　the　hollow　nanocages.　Importantly,　the　synthetic　strategy　can　be　generalized　to　engineer　the　functions　and　properties　of　the　designed　yolk-shell　nanocages　by　varying　the　structure　of　the　COF　shell　and/or　the　composition　of　the　core　MNPs.　Representative　Pd@H-TpPa　yolk-shell　nanocages　with　active　Pd　NP　cores　and　permeable　TpPa　shells　exhibit　high　catalytic　activity　and　stability　in　the　reduction　of　4-nitrophenol　by　NaBH4　at　room　temperature.