The present invention provides a composite phase change material for a battery, wherein the composite phase change material comprises water and a polar organic solvent dissolved in the water, and further optionally comprises an inorganic salt dissolved in the water, nanoparticles dispersed in the water, and a surface modifier. The present invention further provides a composite phase change material preparation method and a battery module adopting the composite phase change material. The composite phase change material can meet cooling requirements of IGBT modules with different powers. In addition, during a phase change process, the composite phase change material produces low stress to a sealing device so as to easy seal, and an IGBT module cooling effect is good.