Organic solid-liquid phase change material can release or absorb a lot of latent heat when its phase state changes. The application of phase change materials in buildings can reduce indoor temperature fluctuations, improve indoor thermal comfort and reduce building energy consumption. Binary phase change material of capric acid (CA) and octadecanol (OD) was prepared by melting blending method. The optimal mass ratio of eutectic mixture is determined as mCA∶mOD=85∶15 by theoretical prediction and step cooling curve. Thermal properties, cycle thermal stability, heat resistance and structure characteristics of CA/OD composite were analyzed by differential scanning calorimetry, heat storage and release experiment, thermogravimetric analysis and Fourier infrared spectroscopy. The melting and solidification temperatures of CA/OD eutectic mixture are 27.95 and 25.42 ℃, respectively, and the latent heat of melting and solidification are 154.2 and 157.0 J/g, respectively. Its thermal properties change little during 300 cycles of heat storage and release, and it has good thermal cycle stability, good heat storage and temperature control performance.Thermogravimetric analysis shows that the CA/OD binary eutectic mixture has no thermogravimetric phenomenon below 125.7 ℃, and has good heat resistance. Fourier infrared spectroscopy analysis shows that CA and OD are combined by physical action, and no new substances are produced in the eutectic mixture. Comprehensive analysis shows that the CA/OD binary composite phase change material is suitable for operation at 24~30 ℃ range of room temperature, meets the comfortable temperature range of human body basically, and has strong cycling durability under the daily thermal environment, which provides a new choice for building energysaving materials.