In this paper the phase transition temperature of epitaxial ferroelectric thin film is analyzed and discussed systematically via the dynamic Ginzburg-Landau (DGL) equation by taking the effective interior stress, surface eigenstrain relaxation and depolarization field. When the thickness of ferroelectric film is changed, external and internal factors, which affect phase transition temperature of ferroelectric thin films,are presented to explain the experimental observations. There is a good quantitative agreement between the theoretical results and experimental data for BaTiO3 thin film epitaxially grown on SrTiO3 substrate.