Micro-Pulse Lidar (MPL) systems provide continuous, automatic observation of nearly all significant atmospheric clouds and aerosols. Being compact in structure and with eye-safe transmitted radiation, the systems proved reliable in a number of experiments both at home and abroad (such as ACE-2 and Aerosols99). An introduction to the structures and working principles of MPL systems, as well as their advantages over traditional ones, are given. The retrieval methods of lidar-determined aerosol optical properties (such as slope, near-end, far-end and iteration methods) and their advantages and disadvantages,and a summary of application researches of MPL to ABL and aerosol measurement, etc., are presented.