This paper presents a new method about how to classify different types of aerosols by lidar measurements. Two lidar equations containing the optic parameters (backscatter coefficient, extinction coefficient ) about two different types of aerosols, background aerosol and cloud, were built. The solutions about the two lidar equations, optic parameters inversion, were given to classify the background aerosol and cloud. The lidar signals generated from backscatter of two different types of aerosols, with two different extinction to backscatter coefficient ratio ( Saer1, Saer2), were simulated, and the optic parameters inversion from the two simulated lidar signals were almost identical to the simulation parameters for different types of aerosols. Two types of aerosols, the background aerosol and cloud, were simultaneously measured by lidar, and were obviously discriminated by using this new method. The simulations and measurements results verified the new method for aerosols classifications.