In this paper, the temperature and reaction source gas flow of growing α-Ga₂O₃ by hydride vapor phase epitaxy (HVPE) were optimized by numerical simulation. Different from the traditional reaction chamber in which Ga source carried by HCl or Cl₂, we use the method of external Ga source, which can accurately adjust the component proportion, mole fraction and concentration of GaCl/GaCl₃. In addition, the activation energy of the reaction between GaCl₃ and O₂ was calculated by molecular simulation software Gaussian, and the activation energy of α-Ga₂O₃ convert to β-Ga₂O₃ was obtained by fitting the experimental data. On this basis, we researched the growth temperature and the composition ratio of GaCl/GaCl₃, and then we concluded the optimal growth conditions of HVPE α-Ga₂O₃.