The　atmospheric　PM2.5　samples　in　urban　of　Beijing　were　collected　in　January　and　July,　2015,　which　represented　the　winter　and　summer　respectively.　The　samples　were　analyzed　for　the　mass　concentration　changes　and　pollution　characteristics　of　PM2.5,　organic　carbon　(OC)　and　elemental　carbon　(EC),　combining　with　relevant　meteorological　data.　Moreover,　the　mass　concentrations　of　secondary　organic　carbon　(SOC)　were　estimated　by　ρ(OC)/ρ(EC)　minimum　ratio　method,　and　the　effect　of　air　mass　transport　on　haze　formation　was　studied　by　using　of　backward　trajectory　and　cluster　analysis　model.　Results　showed　that　the　mass　concentrations　of　PM2.5　and　carbonaceous　aerosol　were　expressed　as　winter>summer,　haze　weather>non-haze　weather.　SOC　is　an　important　part　of　OC,　accounting　for　47.16%　in　winter,　55.54%　in　summer,　respectively.　The　air　mass　trajectories　in　haze　weather　in　winter　were　mainly　controlled　by　northwest　high　air　mass　and　local　air　mass,　among　which　the　local　air　mass　transport　from　Beijing-Tianjin-Hebei　(BTH)　region　was　a　great　contribution　to　the　haze　pollution.　While,　the　air　mass　trajectories　in　haze　weather　in　summer　were　mainly　affected　by　southeast　air　mass,　northwest　air　mass　and　southwest　air　mass.　The　frequency　of　air　mass　trajectories　from　the　south　was　higher　and　have　a　greater　contribution　to　haze　pollution.　Therefore,　strengthening　the　air　pollution　joint　prevention　and　control　in　Beijing-Tianjin-Hebei　and　its　surrounding　areas　is　of　great　significance　for　improving　air　quality　in　Beijing.　©　2018,　Editorial　Department　of　Journal　of　Beijing　University　of　Technology.　All　right　reserved.