Due to their spontaneous polarizations, ferroelectric materials have excellent dielectric, piezoelectric, pyroelectric properties, which enable them to be employed in many applications, such as capacitors, filters, sensors, detectors, and transducers, etc. In this paper, we use a first-principles-based effective Hamiltonian method to investigate perovskite SnTiO3, obtain essential coefficients for the effective Hamiltonian via ab initio computations, which are used in subsequent Monte-Carlo simulations to predict the phase transition temperature of SnTiO3, and different structural phases involved in such phase transition.