Abstract: In this study,GRIMM180 was used to continuously observe the atmospheric aerosol number concentration in the section 0. 25 ～ 32 micron particle size in the downtown area of Nantong city and analyze its variation characteristics from December of 2017 to November of 2018. The number concentrations of spring,summer,autumn and winter were 396/cm³,281/cm³,265/cm³ and 519/cm³,respectively. In spring,the daily changes of PM_1-32 demonstrated a single peak distribution,and the peak occurred at 11∶ 00 am. In summer,the daily changes of PM_{0. 25-1} and PM_{2. 5-32} showed a single peak distribution,and the peak was at the time of 12 ∶ 00 am,which is closely related to solar radiation. The daily changes of PM_{0. 25-32} both in autumn and winter demonstrated both peaks,the peak happened between 8∶ 00 ～ 10 ∶ 00 am and 18 ∶ 00 ～ 19 ∶ 00 pm,which were affected by morning and evening peaks. The peak values of the four seasons number-concentration spectrum of aerosols were 0. 29 micron,and the number-concentration was mainly contributed by fine particles under 1 micron,while the contribution of coarse particles was very little. The concentrations of particles greater than 1 micron remained relatively low. As the concentration of small particles increased,the decline of air quality became more prominent,especially those between 0. 5 and 1 micron.