High energy particle bombardment in silicon carbide will lead to defect accumulation and lattice disorder, which will affect the physical property and do harm to the lifetime of SiC devices. Therefore, it is necessary to systematically study the damage of SiC in different radiation environment. In this work, 6H-SiC was irradiated by neutrons at the fluence of 5.74×10 18 , 1.74×10 19 , 2.58×10 20 and 1.27×10 21 n/cm 2 , respectively, and then annealed. Changes in lattice parameter from post-irradiation isochronal annealing 30 min between 500 ℃ and 1650 ℃ were measured using X-ray single crystal diffraction. The results showed that the lattice swelling and recovery behavior were isotropic. Based on the swelling data, the neutron irradiation-induced defects in 6H-SiC were considered to be primarily point defects. Both intrinsic and irradiation defects introduce defect energy levels. The defect energy levels were mainly caused by the vacancies, which lead to the absorption band edge redshift and band gap narrowing of SiC. The energy levels of these vacancies and vacancy-associated defects were determined by absorption spectroscope, luminescence spectroscope and Raman spectra. The detailed experiments and first principles calculation proved that the silicon vacancies introduced defect levels above the valence band, while the carbon vacancies introduced levels below the conduction band. The infrared absorption at 1382 nm and 1685 nm and the emission at 550 nm of the unirradiated 6H-SiC were mainly due to the intrinsic carbon vacancies. The luminescence of post-irradiated SiC at 415 nm, 440 nm and 470 nm was mainly due to the silicon vacancy produced by irradiation and its related defect configuration. The luminescence mechanism of SiC