A novel high-spectral-resolution lidar (HSRL) technique for atmospheric aerosol remote sensing, which uses multi-longitudinal-mode laser as the transmitting light source, is proposed. A field-widened Michelson interferometer (FWMI) is used as the spectral discriminator, and the periodic frequency discrimination characteristic in the process of FWMI designing should match with the mode interval of multi-longitudinal-mode laser to ensure consistent fine spectral discrimination for the return signal from each longitudinal mode laser. The principle and the realization way of the proposed multi-longitudinal-mode HSRL are illustrated in detail and the main factors which constrain the frequency discrimination characteristic of the FWMI in multi-longitudinal-mode HSRL are discussed quantitatively. The performance of the proposed technique is verified further at the wavelength of 1064 nm by computer simulation. The multi-longitudinal-mode HSRL technique can avoid the dependence of the current HSRLs on the single multi-longitudinal-mode lasers remarkably. The proposed technique can not only decrease the cost, volume and weight of the laser in HSRL, but also improve its stability notably, which is of great significance for airborne and satellite-borne HSRL development in our country.