The　Beijing-Tianjin-Hebei　(BTH)　region　in　the　North　China　Plain　(NCP)　is　significantly　affected　by　inter-district,　city　and　region　transport,　but　systematic　works　on　this　aspect　using　flux　calculation　method　remain　insufficient.　To　obtain　further　insights　into　the　temporal　and　spatial　characteristics　of　PM2.5　flux,　the　Weather　Research　and　Forecasting　(WRF)　model　and　the　Comprehensive　Air　Quality　Model　with　Extensions　(CAMx)　have　been　applied　during　January,　April,　July　and　October　2016.　The　results　demonstrated　that　the　modeling　flux　calculation　method　was　suitable　for　investigating　the　evolutionary　trend　of　PM2.5　flux　by　comparing　cross-district　simulations　and　observations.　The　total　of　monthly　inflow,　outflow　and　net　flux　indicated　the　intensive　interactions　and　prominent　temporal　and　spatial　variations　of　PM2.5　transport　though　the　boundary　segment　of　the　district,　city　and　region.　The　vertical　distribution　analysis　of　net　flux　shows　that　PM2.5　net　flux　between　target　megacity/region　and　surroundings　differed　with　the　altitude,　and　the　altitude　at　which　its　maximum　intensity　was　closely　related　to　neighboring　areas　and　occurrence　of　month.　Notably,　three　main　transport　pathways　during　four　months　have　been　identified　based　on　the　investigation　of　cross-city　transport,　namely　the　northwest-southeast　(NW-SE)　for　January　and　April,　the　southeast-northwest　(SE-NW)　for　July　and　October,　the　southwest-northeast　(SW-NE)　for　all　months,　which　were　further　confirmed　by　cross-region　transport.　Additionally,　summer　and　winter　monsoon　have　significant　influences　on　the　SE-NW　and　NW-SE　pathway,　respectively.　Furthermore,　this　research　draws　upon　a　typical　process　of　PM2.5　haze　episodes　from　11　to　17　October　in　Beijing,　Tangshan　and　Shijiazhuang,　with　the　aim　of　demonstrating　flux　intensity　variations　in　different　stages　of　haze　episodes.　Overall,　the　evolution　of　flux　intensity　at　the　higher-altitude　layer　have　similar　pattern　to　that　of　lower-altitude　layer,　in　which　the　former　was　approximately　2　times　the　latter.　Furthermore,　inter-city　transport　along　the　SW-NE　pathway　played　a　crucial　role　before　reaching　the　most　severe　stage　of　pollution,　while　the　local　emissions　were　more　conductive　to　forming　heavy　pollution　extremes.　Overall,　flux　intensity　calculations　provide　scientific　support　to　put　forward　effective　joint　control　measures　and　acquire　a　better　understanding　of　evolutionary　mechanism　of　haze　episodes　in　the　NCP.