Abstract: Based on the data of daily direct solar radiation during clear days from 1958 to 1989 over Beijing, the atmospheric aerosol turbidity parameters β over this area are calculated. And by combining the results above with the data of coal consumption of the market, weather conditions and volcanic eruptions, the features of annual and interannual changes ofβ and their causes are estimated. The results show that the maximum values ofβ occur in spring and the minimum in the season between autumn and winter; the values ofβ from 1958 to 1997 changed slowly and maintained a range of values between 0.08 and 0.12; after 1978 the values increased rapidly. And generally, the values ofβ in the heating seasons are smaller than that in the other time.