As an energy carrier, the phase change material can enhance the efficiency of an energy source and reduce its load. The present paper describes the assembly of the energy carrier molecule [stearic acid (SA)] into the interlayer spacing of montmorillonite (Mt). A novel inorganic/organic composite energy storage material was prepared, which effectively reduces the phase change temperature of the energy storage molecule. Through acid treatment, the Si4+/Al3+ ratio of Mt can be regulated to obtain a series of Mts with different layer charges. As a result, a controllable assembly of energy storage molecule, SA, into the interlayer spacing of Mts with different layer charges was accomplished. By controlling the layer charges of Mt arrangement morphology and interactive force of SA molecules in the interlayer, spacing of Mt can be changed effectively. The phase change temperature (exothermic reaction) reduces from 50.5 to 32 °C compared with the SA molecules, which are used to control phase change temperature of the energy storage material. The study presents a SA/Mt energy storage material that can aid in further development in the field of energy storage construction materials.