Abstract: Thermal interface materials (TIMs) play a vital role in the thermal management of electronic devices and can significantly reduce thermal contact resistance (TCR). The TCR between the solid–liquid contact surface is much smaller than that of the solid–solid contact surface, but conventional solid–liquid phase change materials are likely to cause serious leakage. Therefore, this work has prepared a new form-stable phase change thermal interface material. Through the melt blending of paraffin wax (PW) and low-density polyethylene (LDPE), the stability is improved and it has an excellent coating effect on PW. The addition of aluminum (Al) powder improves the low thermal conductivity of PW/LDPE, and the addition of 15wt% Al powder improves the thermal conductivity of the internal structure of the matrix by 67%. In addition, the influence of the addition of Al powder on the internal structure, thermal properties, and phase change behavior of the PW/LDPE matrix was systematically studied. The results confirmed that the addition of Al powder improved the thermal conductivity of the material without a significant impact on other properties, and the thermal conductivity increased with the increase of Al addition. Therefore, morphologically stable PW/LDPE/Al is an important development direction for TIMs.