That choosing phase-change material bases on phase-change temperature. In the case of the drop in temperature aim, first of all, to elect phase-change temperature in series, then choose phase-change materials. Adding the fitting proportional core reagent and dense reagent in the tacts, so as to solve the main phase-change material problems; overcooling and layer-built. Finally, this paper documents that choosing, testing and making the suitable two phase-change material systems which are Ca(NO_3)_2.4H_2O +...