A phase transition material, an acrylic monomer and a free-radical initiator are dissolved in an organic solvent to form an oil-phase solution. The acrylic monomer, having bi-functional and/or tri-functional groups, undergoes free radical polymerization to form the microcapsules shells encapsulating the phase transition material. A surfactant is dissolved in water to form a water-phase solution, and the HLB value of the surfactant is eight to twelve. The oil-phase solution and the water-phase solution are mixed and stirred to form an emulsion solution. The emulsion solution is then heated stepwise to form the microcapsules encapsulating the phase transition material.