The temperature dependence of the dielectric constant of monomer single crystal TS has been determined for the range 77-300 K, two anomalies have been observed near 160 K and 203 K. The variation of the dielectric constant of TS during thermal solid state polymerization is obtained. It the initial stage of polymerization, the dielectric constant decreases slowly; when sample conversion to polymer exceeds 30%, the dielectric constant increases rapidly. We suggest that this behavior may be related to side-group and π-electron and hend explain the results qualitativly.