GaTe is a two-dimensional III-VI semiconductor with suitable direct bandgap of～1.65 eV and high photoresponsiv-ity, which makes it a promising candidate for optoelectronic applications. GaTe exists in two crystalline phases:monoclinic (m-GaTe, with space group C2/m) and hexagonal (h-GaTe, with space group P63/mmc). The phase transition between the two phases was reported under temperature-varying conditions, such as annealing, laser irradiation, etc. The explicit phase transition temperature and energy barrier during the temperature-induced phase transition have not been explored. In this work, we present a comprehensive study of the phase transition process by using first-principles energetic and phonon calculations within the quasi-harmonic approximation framework. We predicted that the phase transition from h-GaTe to m-GaTe occurs at the temperature decreasing to 261 K. This is in qualitative agreement with the experimental observations. It is a two-step transition process with energy barriers 199 meV and 288 meV, respectively. The relatively high energy barriers demonstrate the irreversible nature of the phase transition. The electronic and phonon properties of the two phases were further investigated by comparison with available experimental and theoretical results. Our results provide insightful understanding on the process of temperature-induced phase transition of GaTe.