Based on fractal theory, Monte Carlo method is used to simulate the structures of mixed agglomerates in random distribution. The equivalent complex refractive index of internal mixture of agglomerates containing different volume fractions of black carbon particles is obtained by Bruggeman effective medium theory. The extinction characteristic quantities including the absorption, scattering and extinction efficiency factor of mixed agglomerates in internal and external mixing states are calculated based on the discrete dipole approximation (DDA) method. Meanwhile, the influence of mixture patterns, volume content, solar radiative wavelength, the monomer diameters, and the number of monomers on the radiative properties of mixed agglomerates is mainly discussed. Comparison of the numerical results obtained by the DDA method with T matrix method shows that the numerical results obtained by two numerical methods are very similar. The results show that the scattering efficiency factor is substantially sensitive to mixing patterns, the extinction efficiency factor is weaker, while the absorption efficiency factor is not sensitive. The influence of mixing patterns on the scattering and extinction efficiency factor is becoming more obvious with the increase of the size of mixed agglomerates. The absorption, scattering and extinction efficiency factor of mixed agglomerates in internal and external mixing states increase monotonically with the increasing of the volume fraction of black carbon, and the increase varies with the size parameters of mixed agglomerates.