The effect of atmospheric fluctuation on two lidar return signals may be different for quasisimultaneous emission of two lidar wavelengths. The known atmospheric correction methods based on the same atmospheric effects of two laser signals are not suitable for quasisimultaneous emissions of two lidar wavelengths. A new correction method of atmospheric backscattering is proposed. Two backscattering coefficients are computed respectively for differential absorption lidar by Klett technique, and the backscattering correction is calculated. This method is applied to AML-2 lidar data processing for measuring ozone, and experimental results show that this correction method is feasible and reasonable.