Carbon sponge can be used as a carrier for phase-change materials due to its advantages of low density, large pore volume, and high thermal conductivity. A carbon sponge with certain graphitization characteristics and a porosity of 96.30% was synthesized as a carrier with absorbent cotton and MgO as raw materials, and a composite phase-change material encapsulated by a porous carbon sponge was prepared with Na₂SO₄·10H₂O/Na₂HPO₄·12H₂O as a phase-change medium. The results show that the adsorption amount of carbon sponges prepared at 700, 800 ℃ and 900 ℃ to the phase-change materials is 60, 75 and 102 times greater than their weights, respectively. Also, the solid-liquid phase-change cycle performance of the carbon sponge-encapsulated materials prepared at different temperatures was discussed at 5–60 ℃. After 5 000 cycles, the latent heat of the phase-change material is still > 200 J·g^–1, which is reduced by 13%, and the thermal conductivity increasing rate is > 50%. The composite phase-change material encapsulated by porous carbon sponge has promising application prospects in the field of solar energy storage.