The aerosol asymmetry factor (g) is one of the most important factors for assessing direct aerosol radiative forcing (DARF) and remote sensing. So far, few studies have focused on the measurements and parameterization of g. Our study shows that relative humidity has significant impacts on g and DARF due to aerosol hygroscopic growth. For the first time, a novel method based on measurements from the humidified nephelometer system is proposed to calculate g accurately with high time resolution.