Informations about the optical and hygroscopic properties are important for understanding the haze formation mechanism. In order to detect the optical properties and hygroscopic behavior of atmospheric aerosol in fog and haze days under the background of environmental relative humidity change, two cases of typical fog and haze days in Hefei area are studied as examples, and aerosol extinction coefficient, visibility, the Angstrom wavelength index and extinction coefficient hygroscopic growth factor are obtained by using horizontal detection of dual-wavelength lidar. Case study results show that the lidar, with the advantage of detecting unperturbed and ambient atmospheric conditions, can effectively gain the change rule of fog aerosol optical parameters of the hygroscopic absorption and growth factor varying with relative humidity.