Abstract：By using observational data including surface meteorological elements， air quality parameters and the vertical aerosol lidar observation data from Guangzhou Haizhu Lake Atmospheric Composition Station during September to October 2019， the article studied the diurnal cycle of meteorological elements， atmospheric pollutants and the distribution of boundary layer aerosol corresponding to different types of PM2.5-O3 episodes. The causes of high PM2.5-high O3 were further analyzed. A total of 25 days of low PM2.5-low O3 days （Clean Days）， 12 days of low PM2.5-high O3 days （Episodic Days Ⅰ） and 20 days of high PM2.5-high O3 days （Episodic Days Ⅱ） were identified during the observation period. The analysis of meteorological elements and atmospheric pollutants showed that on Episodic Days Ⅱ the average temperature （T） and relative humidity （RH） were over 30 ℃ and lower than 60% from 11：00 to 16：00， and the average daily wind speed （WS） and the maximum J（NO2） were 0.88 m·s-1 and 0.007 s-1， respectively. Compared with Clean Days， Episodic Days Ⅱ is represented by high T and low RH. Meanwhile， slightly lower actinic radiation and lower WS can be found in Episodic Days Ⅱ than Episodic Days I. The daily mean PM2.5 and O3 concentration were 2.3 and 1.5 times of those on clean days， corresponding with the high concentration of SO2 and NO2， high atmospheric oxidation capacity and fine particles ratio on Episodic Days Ⅱ. The lidar results showed that the aerosol extinction coefficient of Clean Days and Episodic Days Ⅰ were lower， and mainly in the range of 0.1~0.2 km-1. In Episodic Days Ⅱ， the aerosol extinction coefficients were in the range of 0.2~0.3 km-1 and the maximum value was below 500m. In the afternoon， the aerosol depolarization ratio in Episodic Days II was larger than that of Clean Says and Episodic Days Ⅰ， indicating obvious feature of secondary aerosol generation. The analysis of typical pollution episodes on Episodic Days Ⅱ shows that the boundary layer evolution could directly affect the distribution of surface pollutants. In the context of Western Pacific Subtropical High and typhoon periphery， the downward transport of pollutants inside the residual layer had a significant influence on the accumulation of surface pollutant concentration in the morning.