The electronic structure and optical properties of 4H-SiC bulk, pristine (0001) surface and the (0001) surface with defects have been studied by the first principles plane wave method. The results showed that 4H-SiC is an indirect semiconductor with the band gap of 2.045 eV, the pristine (0001) surface was an indirect n type semiconductor with the band gap of 0.65 eV, the (0001) surface with defect of carbon vacancy (V-C) was an indirect p type semiconductor with the band gap of 0.46 eV, the (0001) surface with substitution Si for C (Si-C) was a semimetal. The optical properties of 4H-SiC were modulated by the electronic bonding types of Si 3p and C 2p. The calculation provided theoretical reference for the study of 4H-SiC. (C) 2017 Elsevier B.V. All rights reserved.