The reserves of heavy oil far exceed those of conventional oil， but heavy oil is difficult to exploit due to its high viscosity and density. Thus， the efficient and economical development of heavy oil has become a research focus in the petroleum field. Hybrid thermal recovery are critical for efficiently developing heavy oil reservoirs， and phase behavior of multi-component thermal fluids are the key to designing and evaluating the development processes of heavy oil reservoirs. Therefore， this paper systematically reviewed the current experimental and theoretical research on phase behavior in multi-component thermal fluids of mixed gas systems and heavy oil-gas systems in hybrid thermal recovery. For phase behavior of mixed gas systems， static methods were employed for experimental tests， and state equations and mixing rules were for theoretical prediction. Meanwhile， the phase test of the binary system composed of common gas molecules such as CO₂， N₂， H₂O， and CH₄ tends to be mature， while there is a lack of test data and prediction models related to multivariate systems. For heavy oil-gas systems， general experimental processes and recent experimental results were summarized to propose a new experimental device concept for accelerating oil-gas phase equilibrium. Additionally，the disadvantages of current theoretical prediction in gas types， gas injection rates， gas diffusion models， and binary interaction coefficients were pointed out. Furthermore， a prospect was presented for studying the phase behavior of multi-component thermal fluids to promote further mechanism research and parameter optimization of hybrid thermal recovery.