Based on fractal theory, the cluster-cluster aggregation (CCA) model is used to simulate the fractal structure of the soot aerosols in random orientation using Monte-Carlo method, and the absorption, scattering and extinction efficiency factors of fractal soot aerosols in random orientation are simulated in the solar radiation spectrum ranging from 0.2 to 10.0 μm of wavelength by the discrete dipole approximation (DDA) method. The influential rules about the solar radiative wavelength, diameter and the number of primary particles on the extinction characteristics of soot aerosols in random orientation are provided. The comparison of the numerical results obtained by the DDA method with T matrix method shows that the results by two methods are very similar which verifies the validity of DDA method. It is shown that the carbon and fly ash aerosols have different influences of extinction characteristics on solar radiation, whose radiative wavelength ranges from ultraviolet to near infrared bands, and the extinction characteristics of solar radiation by soot aerosols are mainly determined by the radius and the number of primitive particles besides the refractive index.