An atmospheric dust aerosol process in Beijing was observed using a series of atmospheric monitoring instruments on March 9th, 2013. The aerosol particle size and vertical distribution characteristics were observed and analyzed with meteorological data before and after this process to study the differences of pollution characteristics between haze and dust. The results indicated that a dry aerosol haze pollution process was dominated by fine particles before the sand-dust period, with ρ(PM_2.5)/ρ(PM₁₀) up to 0.93. Aerosol depolarization ratio of floating dust at 800~2500m altitude from atmospheric transport was 0.35, which is significantly higher than the haze aerosol. Due to the strong winds with cold front, PBL height lifted up to more than 900m, making that the floating dust from outside source diffused down toward the surface and mixed with local dust, which leads to the increase of coarse particles near ground. The hourly value of ρ(PM₁₀) at surface increased to 920μg/m³ when the sand-dust process sustained. During the dust period, the aerosol depolarization ratio raised up to 0.4with distribution of dust aerosol from ground to about 3000m high. Results suggested that the cold front associated with the Mongolian cyclone was the main weather systems generating this dust process, and deepening development of the upper trough as well as the updrafts caused by ground cyclone was the driving force for the dust propulsion and transport.