The geometrical structures, electronic structures and optical properties of the two-dimensional (2D) SiC doped with P with different concentrations are investigated by the first principle method. The results show that, the lattice constant and the bandgap of 2D SiC doped with P gradually decrease with the increase of P doping concentration. The valence band is mainly composed of the hybridization of the electrons of C-2p, Si-3p and P-3p states, while the conduction band is mainly composed of the electrons of Si-3p state. The P doping weakens the covalency and increases the ionic property for the C—Si bond. The P doping expands the optical absorption range of 2D SiC, and makes the absorption coefficient and the refractive index increase with the increase of doping concentration, which indicates that P doping can effectively improve the absorption for both the visible and infrared light.