By using of high-speed photograph techniques, thermogravimetric analysis (TG), differential thermal analysis(DTA) and scanning electron microscope (SEM), the combustion process of fog aerosol and formation of condensation nucleus were investigated. Results show that the high temperature and pressure air mass with a large amount of high temperature condensation nucleus is produced after the combustion of fog aerosol,and the temperature and pressure decrease rapidly with the air mass ascending. The particle size distribution of condensation nucleus is 0.2-1 μm and its main component is NaCl. The growing process of condensation nucleus and the forming of fog droplet are related with the supersaturation produced by the cooling and expanding of the air mass.