A DPT ferroelectric ceramics system of (Ba1-xLax)(Ti1-yZry)O3 and a DPT-SPT ferroelectric crystal serise of K0.2Na0.2(SrpBa1-p)0.8Nb2O6 have beenprepared by the ordinary ceramics manufacture technique and Czochralski technique respectively. The curves of dielectric constant vs. temperature of all samples have been measured. The semi-quantitive point-analyses of composition distribution have been obtained by the technique of SBM and EDAX. The inhomogeneity of composition distribution was discovered in both DPT ceramicses and DPT single crystal, but in SPT crystal no such fluctuation was found. It was shown that the diffuse curves of ε(T) is related to composition fluctuation directly. Therefore the Smolensky's composition fluctuation model for DPT was proved in experiment. According to this model, there is a statistical distribution of transition temperature, inside the DPT ferroelectrics. The theoretical calculation of dielectric constant with the change of temperature of all samples were done by using two different expressions of ε′(T, Tc). The theoretical results agree well with experimental curves.