A sodium acetate trihydrate (SAT)-urea binary eutectic mixture was developed as a phase change material (PCM). Using the differential scanning calorimetry (DSC) experiment and synthetic visual method, the solid-liquid phase diagram of SAT-urea was obtained, through which the eutectic composition of SAT-urea binary mixture was determined. The results show that the binary eutectic point composition formed by 60 wt % SAT and 40 wt % urea melted at the temperature of 31.4 degrees C with a latent heat of 205.3 J/g. XRD, FTIR, H-1 NMR, and DFT calculation results show that the interactions of SAT and urea were intermolecular hydrogen bonds, and no clear chemical interactions were observed. The modification of SAT-urea eutectic PCM was studied by the uniform experimental method. The results show that for the SAT-urea eutectic with 3 wt % disodium phosphate dodecahydrate (DSP) and 2.18 wt % carboxymethyl cellulose (CMC), the supercooling degree is decreased to 2.9 degrees C, which is consistent with the calculation results. After 50 thermal cycles, SAT-urea eutectic PCM exhibits good thermal stability and reliability.