The soliton behavior of K2ZnCl4 crystal near commensurate-incommensurate phase transition point is investigated by dielectric measurement. It is found that the dielectric curve deviate from Curie-Weiss law and the dielectric peak value decrease with the increasing of the impurities. The influence of impurities on phase transition point Tch in heating run is larger than phase transition point Tcc in cooling run. This phenomenon is contrary to the case of Rb2ZnCl4 crystal. The linear and nonlinear response of a multisoliton lattice is well described by a Landau-type theory. Analysis shows that the thermal hysteresis is mainly determined by the action of impurities, but this does not imply that the Peierls lattice pinning potential may not play any role in the thermal hysteresis.