To study the pollution characteristics of PM2.5 during the haze period in October 2014, the hourly automatic monitoring data and 22-h atmospheric PM2.5 samples were collected in Changchun city. According to the statistical results of the hourly average PM2.5 concentration, heavy pollution occurred from October 13 to November 1 in 2014 in Changchun city. The daily concentration of PM2.5 during this period was 53.18 µg m–3 to 450.69 µg m–3. In addition, the PM2.5 concentration was higher at night and lower during the daytime on haze days, which is affected by pollutant emission and meteorological conditions. The Pearson correlation coefficient between PM2.5 and CO was high (r = 0.745), which implies that the concentration suddenly increased, probably because of the combustion of fossil fuels and other organic matter. The meteorological condition investigation shows that the wind speed, temperature and pressure are low and that the RH value is relatively high on haze days. In addition, stable weather during haze days makes the pollution heavier. The analysis of water-soluble inorganic ions (WSIIs) suggests that WSIIs constituted up to 21–56% of PM2.5, and the total ions, anions and cations showed a significant correlation. During the haze days, the NO3–/SO42– ratio was substantial (3.7–4.6), except at the CP and JZP stations, which suggests that the pollutants in the atmosphere are from a mixture of stationary emission and mobile emission. The NOR and SOR values were more than 0.1 at most sampling stations, so serious secondary pollution occurs in the atmosphere on haze days, and secondary ion formation is enhanced by the atmospheric conditions and emissions of gaseous SO2 and NO2.