Abstract: Huff and puff stimulation with multiple thermal fluids is a kind of new enhanced heavy oil recovery technology, and this heavy oil recovery technology has been used in NB-XX oilfield in Bohai Bay, with good oil recovery results. However, it is not clear about the viscosity reduction and enhanced oil recovery mechanism. Through matheraatic simulation and laboratory experiments, the mechanism of multiple thermal fluids has been analyzed. Through this study, the mechanisms of increasing heavy oil productivity in individual well with multi-thermal fluids and improving heavy oil development effects have been made clear. It provides a theoretical basis for the application of this technology to other heavy oil fields.