Abstract: To address the problem that the surface effect of nanoparticles affects their thermodynamic properties, a method of introducing the size of nanoparticles into the calculation of surface energy is proposed. Firstly, the size of the nanoparticle was introduced into the calculation of surface energy, and a size-dependent thermodynamic model of nanoparticle was obtained. Then, the thermodynamic parameters of bismuth nanoparticles were brought into the model, and the relationship between surface energy and surface Gibbs free energy of bismuth nanoparticles with particle size, temperature and other variables was obtained. The size of bismuth nanoparticles has significant effects on their surface energy, surface Gibbs free energy, melting temperature, melting enthalpy and melting entropy. The accuracy of the model was evaluated by machine learning support vector regression, and the relative error is within 3%, and the results show that the model can effectively evaluate the thermodynamic properties of nanoparticles.