Abstract: Based on the thermodynamic theory, the critical phase transition temperature of 1-3 type multiferroic composite BaTiO₃-CoFe₂O₄ was investigated by linear stability analysis, Taking into account the coupled elastic stress on the interfaces of ferroelectric/ferromagnetic phases and film/substrate, the analytic expressions of para-ferro transition temperature of the epitaxial multiferroic composite thin film were derived as a function of volume fraction, lattices parameters, material constants and thin film thickness, The results show that the critical phase transition temperature can be controlled by adjusting the volume fraction or thickness of the composite thin film.