The nonstoichiometric β-SiC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator.The prepared powders were invistigated by XRD and Raman spectra.The results indicates that the cell parameters of all the prepared β-SiC powder are smaller than the standard value of β-SiC because of generation of CSi defects.The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz.It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content.The effect of CSi defects on dielectric property of β-SiC powder has been discussed.