Insightful understanding of the light driven CO2 reduction reaction (CO2RR) mechanism on gold nanoparticles is one of the important issues in the plasmon mediated photocatalytic study. Herein, time-dependent density functional theory and reduced two-state model are adopted to investigate the photoinduced charge transfer in interfaces. According to the excitation energy and orbital coupling, the light driven mechanism of CO2RR on gold nanoparticles can be described as follows: the light induces electron excitation and then transfers to the physisorbed CO2, and CO2 can relax to a bent structure adsorbed on gold nanoparticles, and the adsorbed C-O bonds are dissociated finally. Moreover, our calculated results demonstrate that the s, p, and d electron excitations of gold nanoparticles are the major contribution for the CO2 adsorption and the C-O dissociation process, respectively. This work would promote the understanding of the light driven electron transfer and photocatalytic CO2RR on the noble metal.