Based on the transition feature in procedure of producing stacking fault in hexagonal close-packed (hcp) metals that the atoms arrangement changes from AB (hcp) to ABC (fcc), the stacking fault energy (SFE) of hcp metals has been calculated from the energy of phase transition. In addition, the factors of vacancy defect and temperature have also been taken into account. Based on the thermodynamic model of stacking fault energy, the SFE of pure hcp metals Mg, Zn and Ti has been calculated. The equation of the influence of temperature on the SFE has also been established and finally the values of the equation have been calculated. The result shows that the thermodynamic model is fit perfectly for the pure hcp metals and the calculated results agree with the results calculated by first principle. The SFE of hcp metals is decreased gradually with the increasing temperature. The chemical free energy is also the key influence factor on SFE. In addition, vacancy can reduce the stacking fault energy of pure metals. The density of vacancy is increased with the increasing temperature and the devotion to the change of SFE is also increased.