The relation of Debye temperature with the interaction potential of atoms, the r elation of the mean coordination number with the shape and atomicity are deduce d. Through applying the theory of statistical physics, the variation law of the surface energy of rectangular nanocrystals along with the temperature, atomicit y and shape is obtained, and taking Ar nanocrystal as an example, the influence of shape and atomicity on the surface energy of the nanocrystal is discussed.