In order to determine the relative humidity (RH) impact on the aerosol Angstrom exponent (AE), a twowavelength lidar is employed to observe the aerosol AE, two typical case studies have been given at Hefei area based on the wind direction, one represents pollution aerosol case, and the other represents rural aerosol case. The result indicates that during the two cases the RH has a strong effect on the variety of the AE, but totally different correlation between the two parameters can be found. During the rural case, the RH is between 49.2%~91.9%, the AE is between 0.75~1.98, and the AE of the pollution case is between 0.2~1.56 when the RH changed between 58.7%~96.0% . The pollution case presents a negative correlation between the RH and the AE, due to the aerosol hydrophilic growth with a Junge distribution. It is noteworthy that the rural case presents a positive correlation between the RH and the AE, the cause of this phenomenon is probably that particle size distribution is multimodal distribution composed of fine particles and coarse particles of dust pollution.