In this paper, models are presented for predicting the melting point and latent hear of low-melting alloys to facilitate the design of PCMs. Based on the characteristics of entropy and enthalpy during the transition of material phase, the prediction model of melting point and latent heat for eutectic binary system are established at first, and then the models are extended into multicomponent system. Calculated melting point and latent heat of 15 selected low-melting alloys are compared with measurement results using DSC, which shows a good agreement between the prediction and the experimental data. A criterion for preparation of metallic PCMs is also proposed that in order to obtain higher latent heat alloy, an element with higher latent heat should be selected as component of alloy, and the mole fraction of the element should be increased. The advantage of the models proposed is that the melting point and latent heat of certain PCM can be predicted mathematically, avoiding the many experiments needed in conventional ways.