Lidar ratio problem is discussed for atmospheric aerosol particle dectection. Lidar ratios at 0.532 μm for slightly non-spherical continental-average aerosol particles are evaluated according to up-to-date database of aerosol optical and micro-physical properties. It is found that the non-sphericality has an obvious impact on lidar ratios. The results could be applied in practical lidar detection of atmospheric aerosol particles.