Abstract: A sand-dust process in Beijing was monitored based on a Lidar system, PM_2.5 and conventional meteorological observation instruments on March 30^th and 31^st, 2012. The aerosol extinction coefficient was retrieved during this process. The vertical structure and transport characteristics of sand-dust aerosol and the concentration of PM_2.5 were analyzed. The results indicated that wind speed increased to 6m/s and the concentration of PM_2.5 at land surface increased to 289μg/m³, when the sand-dust process sustained; meanwhile, the relative humidity and the appearance of haze significantly decreased. The meteorological conditions such as inversion of lower atmospheric and wind speed near the ground greatly impacted on the duration and intensity of the sand-dust. The maximum value of extinction coefficient was 0.96km^-1, while depolarization ratio was 0.4. There was a strong correlation between the aerosol and extinction coefficient at 400m retrieved from the Lidar data. PM mainly originated from local and surrounding areas of Beijing. Sand-dust from Inner Mongolia Province and outer Mongolia area is the main reason to explain the process.