Abstract Solar energy radiation during the midday could causes the internal temperature of building rising, thus resulting in a significant source of power consumption to run air conditioner devices for thermal comfort environment. A growing interest developed in phase change materials (PCMs) applied in building envelope owing to the prevailing energy challenges. A new type of shape-stabilized composite phase change material (CPCM) was developed by introducing a novel Na2HPO4·12H2O–K2HPO4·3H2O (DSP-PPDT) eutectic hydrated salt into super absorbent polymer (SAP), which was characterized by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD), Scanning electron microscope (SEM). Results indicated that DSP-PPDT eutectic hydrated salts in various ratios all can be formed, among which DSP-PPDT eutectic hydrated salt with the mass fraction of PPDT at 25% had a melting temperature of 24.26 °C, making it suitable for building envelope. The results of cooling tests suggested that 2% of Na2SiO3·9H2O nucleating agent could reduce the supercooling degree of the eutectic hydrated salt to 0.79 °C. The modified eutectic hydrated salt could be stabilized in the network structure of SAP at a mass fraction of 12% through physical interaction without leakage, which melted at 24.13 °C with the enthalpy of 172.7 J/g and had enhanced thermal stability, good thermal reliability at 100 thermal cycles as well as low thermal conductivity of 0.474 W/(m·K). The good thermal performances of CPCM make it a promising candidate applied in building envelope.