Based on the diffusion-limited aggregation model, the aggregated soot and its mixture particles with water coating are generated. The aging process of soot aggregates is simulated. The effects of particle morphology and water coating on the optical properties of the two kinds of particles at the wavelength of 550 nm are studied by the cluster T-matrix method. The results show that the difference of optical property parameters between the freshly generated soot aggregate and the spherical soot with the same volume is larger than the difference between the aged soot aggregate and the spherical soot. When the fractal dimension Df is 1.8, the relative differences of scattering cross section and single scattering albedo reach 61.58% and 49.44%, respectively. As the aging process proceeds, the differences decrease. For the mixture particles, ignoring the cluster structure of the soot core can lead to underestimation of the forward scattering intensity, scattering cross section, extinction cross section, single scattering albedo, asymmetry factor, and F34/F11, and overestimation of the backward scattering intensity, absorption cross section, -F12/F11, F33/F11, and F44/F11. With the increase of the water coating thickness, the scattering matrix elements of mixtures are more turbulent with scattering angle, and the relative differences of optical property parameters caused by ignoring the soot core and the aggregated morphology of soot core are both reduced. This study has significance for decreasing the estimation error of radiative forcing estimation due to soot aerosol.