The study by using the observation data (from May to September 2016) of Langfang Atmospheric Monitoring Super Station, the pollution characteristics of PM_2.5, extinction characteristics, source analysis and backward trajectory analysis were carried out. During the observation period, the concentrations of PM_2.5 were (43.82±28.68)µg/m³. SO₄^2-, NO₃^-, NH₄⁺, OC and EC accounting for 24.74%, 22.98%, 20.54%, 8.79% and 5.50% of the mass of PM_2.5, respectively. The concentration of components increased with increment of PM_2.5 concentration. Scattering coefficient (Bsp) and absorption coefficient (Bap) of atmospheric extinction were (294.54±257.35), (16.05±9.14)Mm^-1, respectively, The contribution of the coarse particles to the extinction coefficient (11.12%) was the lowest. PM_2.5 played a major role in atmospheric extinction. Among them, Nitrate (32.23%), Sulfate (27.28%) and OM (20.56%) were the most important extinction components. PM_2.5 mainly from industry (14.14%), motor vehicles (15.15%), secondary sources (38.38%), coal combustion (22.22%) and dust and biomass burning(10.10%). The contribution of various pollution sources to the extinction coefficient was 1.32% (industry), 17.25% (motor vehicle), 55.57% (secondary source), 18.56% (coal combustion) and 7.32% (dust and biomass burning). According to the backward analysis, the small-scale, short-distance transmissions from Shandong and Henan provinces as well as the medium and short-distance transmissions from northeastern and central Inner Mongolia were the major sources of the air mass of Langfang City, which were accounted for nearly 80%. The potential distribution areas of pollution sources were mainly in northeastern Shandong, eastern Henan, eastern Shanxi, and southwest Liaoning.