In this study, the optimized expanded vermiculite (EVM) was used as the matrix and a series of novel form-stable composite phase change materials (fs-CPCMs) were prepared by the physical impregnation method. The results showed that acid leaching and organic intercalation EVM had a better package effect (>= 74.9 wt %) and heat storage capacity (>= 139.2 J/g) compared with EVM, which showed a good optimization effect, revealing that proper modification treatment was beneficial to the improvement of the thermophysical properties of composite PCMs. Nonisothermal crystallization kinetics demonstrated that the EVM matrix was beneficial to reduce the nucleation activation energy (Delta E-alpha) of PEG, and the optimized EVM could further reduce the Delta E-alpha, which effectively improved the crystal nucleation process of PEG. However, the matrix would restrict the crystal growth process of PEG, which had certain adverse effects. Moreover, XRD, TGA, and cycle tests showed that the prepared novel fs-CPCMs had excellent chemical stability, thermal stability, and cycle reliability. This research provided a certain theoretical reference and technical support for the preparation of mineral-based organic composite phase change materials with high heat storage capacity and excellent phase change behavior.