The structural evolution of perovskite phase Pb[(MgxZn1-x)1/3Nb2/3]O3 (abbreviated to PZMN) was found to be highly dependent on its precursors' strong tendency of forming pyrochlore phase in the mixture of raw materials. Three major pyrochlore compositions, Pb2Nb2O7, Pb3Nb2O8 and Pb3Nb4O13, were characterized and analyzed to understand their roles in the formation of the perovskite PZMN phase. Based on phase structure evolution, a preparation method for forming high dielectric constant PZMN ceramics without using common stabilizers such as SrTiO3 was proposed. By using pre-synthesized perovskite PMN, a Zn-rich PZMN composition with an almost 100% perovskite content and a maximum dielectric constant of 22 000 at 1 kHz is obtained. The formation mechanism of PZMN perovskite phase was also reported in this research. The pre-synthesized perovskite PMN acts as stabilizer and nuclei to initiate PZMN perovskite formation through the reaction in the PMN/ZnO interface. A ternary phase diagram of PMN-PZN-SrTiO3 was further constructed to investigate the perovskite development and its related electrical properties.