Analysis of spatio-temporal characteristics and correlations between aerosol optical depth(AOD) and Angstrm exponent over northwest was analyzed based on MODIS C6 product from 2006 to 2015. The results showed that the high AOD occurred in the area of Southern Xinjiang and Guanzhong region of Shaanxi Province, the south of Qinghai and Gansu Province existed low value. High Angstrm exponent occurred in the east of the northwest, and spatial distribution was quite different in the north of Xinjiang. The annual mean AOD was 0.208±0.011, Angstrm exponent was 1.185±0.025. AOD showed a downward trend during 2010 to 2015, and Angstrm exponent was on the rise during 2008 to 2015. AOD and Angstrm exponent were opposite to the seasonal changes, the largest AOD was in spring, the smallest in autumn, just the reverse to Angstrm exponent. The monthly mean AOD appeared in April, which was 0.35 ± 0. 038, the smallest in October was 0.13 ± 0.009, Angstrm exponent was the largest in December, which was 1.34 ± 0.35, the lowest in April was 0.97 ± 0.054; AOD and Angstrm exponent had negative correlation, the highest correlation in spring, which was -0.77, the lowest correlation in winter, which was -0.28. The correlation between AOD and the Angstrm wavelength index in different seasons was analyzed, the results indicated that coarse and fine particle size aerosol particles occupied a certain proportion, mainly in small particle size of the smoke particles, dust aerosol particles also occupy a certain proportion. Aerosol emission was increased from spring to winter.