A Monte Carlo simulation model is proposed to study the phase transition and the structural evolution of thermoreversible gels with the coexistence of phase separation and gelation processes. Our model includes the mobility of all the species and the reversibility of bonds of the clusters formed due to cross-linking reactions. These features provide a more realistic description of a polymer-solvent system. We attempt to elucidate the effects of interactions, solvents, polymer fraction, etc. on the phase behaviors of the thermoreversible gel. Sol-to-gel transition is studied in detail as a function of temperature, and the related critical exponents are evaluated. Two different energy parameters are used to describe the gelation and the melting processes. The collective structure factors are calculated, and their dynamic behaviors are analyzed. The competing effects of the phase separation and the network formation on the structural evolutions of the gel are discussed.