In this paper,Ozone Laser Radar was used for continuous observation of a typical O_3 pollution process in the summer of Nanjing,the variation of O_3 in near-surface air and at high altitude,the pollution causes and process were discussed. Results showed that this typical O_3 pollution was caused by the mixture and accumulation of recycled O_3 in near-surface air and residual O_3 at night sky under the effects of turbulence at hot calm weather and at front before cold air arriving. The O_3 concentration in n...