This　study　applied　the　CAMx　model　to　study　the　regional　transport　of　various　PM2.5　components　in　Beijing　during　a　severe　pollution　episodes.　The　results　revealed　that　during　the　episodes,　Beijing　had　the　average　PM2.5　pollution　value　of　119　mu　g　m(-3).　It　was　1.58　times　of　the　PM2.5　national　air　quality　standard　(75　mu　g　m(-3)　Level　II).　The　wind　speed　was　low　(＜　2　m　s(-1))　and　relative　humidity　reached　98%.　The　anticyclone　in　Eastern　China　showed　weak　local　flow　fields　and　southerly　winds　at　the　surface　and　strong　temperature　inversion　under　1000　m,　which　promote　pollution　accumulation.　The　contribution　of　monthly　regional　transport　to　primary　PM2.5　components　and　SO42-,　NO3-,　and　secondary　organic　aerosol　concentrations　in　Beijing　were　29.6%,　41.5%,　58.7%,　and　60.6%,　respectively.　The　emissions　from　Baoding　had　the　greatest　effect　on　the　primary　components　of　PM2.5　(6.1%)　in　Beijing.　The　emissions　from　Tianjin　had　the　greatest　influence　on　the　secondary　components　of　PM2.5　concentrations.　These　values　indicated　that　the　secondary　components　of　Beijing＇s　PM2.5　are　more　easily　affected　by　transboundary　transport　than　are　the　primary　components.　The　present　findings　suggest　that　control　strategies　for　PM2.5　pollution　should　include　coordinated　efforts　aimed　at　reducing　secondary　aerosol　precursors　(SO2,　NOx,　and　VOCs)　from　long-range　transport　and　local　generation　in　addition　to　primary　particulate　emissions.