Assuming atmospheric molecules extinction coefficient is known, a new method for retrieving aerosol extinction coefficient with pure aerosol echoes is proposed. The pure aerosol echoes are reconstructed with rotational Raman echoes and Mie echoes detected with a rotational Raman-Mie scattering lidar (RRML). Assuming the extinction backscattering ratio is an approximate constant, an integral formula for aerosol extinction coefficient inversion is derived. In the method, the Rayleigh backscattering signal included in the Mie echo is removed to reduce the impact of fluctuation of atmospheric molecules. Finally, the new method is applied to the RRML echo detectinon by the RRML developed by ourselves. The results showe that stable aerosol extinction coefficient profile could be retrieved effectively by using the new method.