Combining CALIOP aerosol optical depth (AOD) products and coincident AODs at two AERONET sites (i.e., Hangzhou－ZFU and SACOL), CALIOP Level 2 column AOD against AERONET AOD is validated. Intercomparison analyses show that the correlation coefficient between AOD at Hangzhou－ZFU (SACOL) and CALIPSO-derived AOD reaches as high as 0.87 (0.85), and the slope of the regression equation is 0.76 (0.92), indicating that CALIOP AOD is better enough to be applied to characterize the regional air pollution. Based on concurrent CALIOP level 3 monthly mean gridded AOD products (daytime and nighttime) and the MODIS Terra/Aqua level 3 monthly mean AOD dataset of the 8 years (2008～2015), the spatial and temporal variations of AOD over Southeast China and Northwest China are analyzed. Results show that Southeast China exhibits a significant seasonal and spatial variability. High AOD values are largely located in Yangtze River Delta and Pearl River Delta. The highest AOD occurs in spring, followed by summer, and then winter and autumn. In terms of monthly average AOD, MODIS tends to overestimate AOD compared with AERONET, ranging from 0.25 to 0.8. CALIOP AOD during night is commensurate with MODIS AOD. By comparison, much difference exists between the daytime CALIPSO AOD and MODIS AOD, which is as high as 0.45. Results from both MODIS and CALIPSO AODs suggest that the spatial distribution of AOD is very similar. To be more specific, the high AOD value is largely located in the Tarim Basin, Junggar Basin and Qaidam Basin. Meanwhile, the highest AOD value occurs in the spring, followed by summer, then winter and autumn. Overall, MODIS AOD values fluctuate significantly and are generally higher than CALIOP AOD values.