Based　on　meteorological　data　and　air　quality　data,　the　characteristics　and　causes　of　a　large-scale　severe　pollution　process　in　Beijing　Tianjin　Hebei　region　and　Yangtze　River　Delta　region　from　December　29,　2016　to　January　8,　2017　were　analyzed.　The　main　meteorological　characteristics　of　the　heavy　pollution　process　were　pressure　field,　low　boundary　layer　height　and　quiet　breeze.　The　end　of　the　heavy　pollution　process　was　due　to　the　higher　pressure　gradient　and　better　horizontal　diffusion　conditions,　Based　on　the　WRF-CMAQ　(Weather　Research　and　Forecasting　Model　and　Community　Multi-scale　Air　Quality)　scenario　analysis　method,　the　effects　of　regional　transmission　and　local　accumulation　on　the　heavy　pollution　process　were　evaluated.　The　analysis　showed　that　in　the　early　stage　of　heavy　pollution　controlled　by　south　wind,　the　Yangtze　River　Delta　region　was　mainly　affected　by　transmission　(15%　~　20%)　from　the　Yangtze　River　Delta,　and　the　Yangtze　River　Delta　region　was　mainly　influenced　by　local　contribution;　in　the　accumulation　stage,　the　local　contribution　of　the　Yangtze　River　Delta　region　decreased　significantly,　while　the　contribution　from　Beijing　Tianjin　Hebei　region　increased　significantly　(20%　~　30%).The　results　showed　that　the　peak　value　of　the　net　transmission　fluxes　fromYangtze　River　Delta　to　Beijing　Tianjin　Hebei　region　occured　in　the　early　stage　of　heavy　pollution　(-21.52t/d),　and　the　peak　value　of　net　transmission　fluxes　from　Beijing　Tianjin　Hebei　region　to　Yangtze　River　Delta　occured　in　the　accumulation　stage　(17.29t/d),　the　regional　transport　effect　was　the　most　active　between　1001　and　1478m.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.