From October 2019 to February 2020, offline sampling was conducted to study the concentration level and mass balance of PM_2.5 in Yancheng urban area, component analysis and source analysis were done as well. The results showed that the monthly average concentration of PM_2.5 in Yancheng city ranged from 43.32 to 62.59 μg/m³, with the highest concentration in January. The average concentration of PM_2.5 was 54.25 μg/m³,the reconstructed value was 52.38 μg/m³, and the correlation with the measured concentration reached 0.98. During the monitoring period, the most important component of PM_2.5 in Yancheng is SNA(SO^2-₄+NO^-₃+NH⁺₄), in which the average value of m(NO^-₃)/m(SO^2-₄) is 2.16, indicating that motor vehicles in Yancheng have a higher contribution to NO₂ and SO₂ than fixed sources during this period. Principal component analysis showed the PM_2.5 of Yancheng city in autumn and winter mainly comes from soil, dust source, combustion source and secondary inorganic source.