The invention belongs to the technical field of building materials and in particular relates to a preparation method and application of a phase change material for an energy-saving building. According to the preparation method disclosed by the invention, the phase change material of a microcapsule structure is prepared by taking tetradeconic acid, capric acid, 2-hydroxyethyl acrylate, methyl methacrylate, alpha, omega-dimethacrylate based polyethylene glycol, chitosan and the like as raw materials. The phase change material of the microcapsule structure prepared by the invention has a phase change temperature of 15.9-26.3 DEG C, and the phase-change potential heat value is 100.6-102.4J/g; moreover, differential scanning calorimetry indicates that the phase change material of the microcapsule structure prepared with the method has excellent thermal stability and remains initial thermodynamic property after 100 times of cool-thermal cycling.