The phase transition temperature and phase transition latent heat of the binary mixtures were measured by differential scanning calorimetric. One of the binary mixtures was composed of 48# paraffin and liquid paraffin, the other one was composed of capric acid and stearic acid. Six kinds of samples were carried on 5000 times of thermal cycling test, so as to choose suitable materials used in the envelope as energy storage materials. The experimental results show that the phase transition temperature and phase transition latent heat have a significant change with different proportion of the mixtures. Their thermal stabilities are good, and the thermal stability of fatty acid mixtures is better than that of paraffin mixtures. The mix proportion of phase change material used in passive phase change wall and active phase change heating floor or wallboard was given as well.