The invention relates to a high-performance solid electrolyte and a preparation method thereof. The chemical expression of the electrolyte is CaHf(1-x)RExO(3-a), wherein the high-performance solid electrolyte is prepared by using CaCO3, HfO2 and an rare earth oxide RE2O3 as raw materials and adopting a technical route including pretreatment, material preparation, pre-grinding, pre-sintering, crushing, final grinding and final sintering. The electrolyte has the advantages of high density, high conductivity, large proton migration number, wide proton conductivity range, high temperature stability, high chemical stability and high corrosion resistance and has excellent comprehensive performance. The electrolyte is used in the technical fields of electrochemical hydrogen sensors, solid oxide fuel cells, hydrogen and heavy hydrogen extraction preparation, hydrogen isotope concentration, organic hydrogenation and dehydrogenation, electrochemical synthesis of ammonia and methanol and the like. The problems can be solved that existing solid electrolytes have low density, narrow proton conduction range, small proton migration number, low chemical stability, poor high temperature stability and the like.