Experimental and theoretical results of the investigation of light induced domain structure changes inside the irradiated region of epitaxial YIG:Co film are given. Dynamics of the effect was investigated using linearly polarized argon laser beam (lambda= 488 run) in pulse regime using Pockels cell. Magnetization changes happen through domain wall shift caused by the presence of light induced spatially inhomogeneous anisotropy energy distribution. Theoretical model was proposed for the magnetic anisotropy description taking into consideration light induced redistribution of strongly anisotropic ions (Co2+ in octahedral positions in our case). Probability of both isotropic thermal and anisotropic polarized light induced excitations of these ions were included in constructed equations. Their numerical solutions gave information about dynamics of Co2+ ions redistribution and afterwards light induced changes of magnetic anisotropy.