［Objective］To address the persistent challenges of leakage failure，thermal cycling instability，and low energy storage density in conventional phase change materials（PCMs）applied to solar energy storage，waste heat recovery，building energy efficiency，and electronics thermal management.［Methods］ This study innovatively proposes a molecular design strategy for polyurethane-based solid-solid PCM（PUPCM） through structural modulation. Specifically，linear main-chain PUPCM（L-PUPCM） was constructed via block copolymerization of hexamethylene diisocyanate（HDI）/urea with poly（ethylene glycol）（PEG），while three-dimensional networked PUPCM（C-PUPCM）was formed through crosslinking reactions between triphenylmethane triisocyanate（TTI） and PEG. Systematic investigations of structure-property relationships were conducted by regulatingfeed ratios［n（PEG）∶n（HDI）∶n（Urea）=1∶2. 2∶0. 2 for linear systems；n（TTI）∶n（PEG）=1∶2.2 for crosslinked systems］ and PEG molecular weights.［Results］ DSC results demonstrated high phase change enthalpies of 157. 8 J/g for linear structures and 125. 3 J/g for crosslinked structures，both exhibiting excellent latent heat. FT-IR analysis confirmed effective immobilization of PEG phase-change units in both materials，with crosslinked structures showing superior dimensional stability.［Conclusion］ This work provides a novel molecular design strategy for developing high-enthalpy， high-stability solid-solid PCMs.