Regional　transport　always　plays　a　crucial　role　in　the　formation　and　dissipation　of　haze　over　the　Beijing-Tianjin-Hebei　(BTH)　region.　This　study,　conducted　using　pollution　and　meteorological　observations　and　the　Weather　Research　and　Forecasting　model　(WRF)　coupled　with　the　Comprehensive　Air　Quality　Model　with　Extensions　(CAMx),　investigated　the　possible　meteorological　causes　for　the　occurrence　of　haze　pollution　and　quantitatively　assessed　the　PM2.5　transport　contribution　to　haze　episodes　that　occurred　in　Beijing　in　January　and　July　2015.　The　results　indicated　that　modeling　system　reproduced　the　spatial-temporal　variation　in　PM2.5　concentrations　in　the　BTH　region　well.　During　the　study　period,　haze　episodes　were　primarily　attributed　to　meteorological　conditions　such　as　planetary　boundary　layer　height,　relative　humidity,　wind　vector,　and　temperature　inversion,　in　the　context　of　pollution　emissions.　Analysis　of　surface　PM2.5　transport　showed　that　62.89%　of　the　surface　PM2.5　in　Beijing　was　came　from　local　emissions,　with　the　remaining　23.69%　and　13.42%,　on　average,　originating　from　short-　and　long-range　transport　during　the　study　period.　The　percentage　of　contribution　varied　with　the　evolutionary　stage　of　the　haze　episodes,　showing　the　joint　influence　of　local　emissions　and　regional　transport　on　haze　pollution　in　Beijing.　Additionally,　investigation　of　vertical　PM2.5　transport　identified　the　following　three　major　pathways:　a　northwest-southeast　pathway　in　January　(at　all　layers　below　1200　m,　though　it　was　stronger　above　600　m),　a　southeast-northwest　pathway　in　July　(at　all　layers　below　800　m),　and　a　southwest-northeast　pathway　during　both　months　(at　a　height　of　200-1200　m).　Moreover,　the　magnitude　of　daily　PM2.5　transport　fluxes　during　the　haze　episodes　was　generally　stronger　than　the　corresponding　monthly　average.　These　results　provide　a　scientific　basis　for　strategic　control　of　both　multiple　cities　and　provinces　and　in-depth　knowledge　of　the　mechanisms　and　sources　of　haze　pollution　in　the　BTH　region.