As the foamy oil phenomenon disappears gradually, the produced gas-oil ratio of foamy oil reservoirs increases rapidly and the well productivity declines fast. This paper presents a new EOR method for foamy oil reservoirs after cold production, called chemical-assisted methane flooding (CAMF), which works with the viscosity reducer slug (naphtha) to improve the mobility of heavy oil in the porous media and then the methane gas and foaming liquid slug to form a secondary foamy oil phenomenon under the action of formation shear and foaming liquid. Experimental studies were carried out to understand the mechanisms of CAMF. First, a high temperature and high pressure (HTHP) rheometer was used to evaluate the viscosity reduction performance of naphtha under different temperatures and naphtha contents. Then, a visual HTHP experimental unit was adopted to identify whether secondary foamy oil would be effectively generated. Finally, a specially designed HTHP microscopic flow experimental unit was adopted to reveal the microscopic flow behaviors and EOR mechanisms of CAMF. The study results show that the CAMF process can form an obvious secondary foamy oil phenomenon, proving CAMF as an effective method to enhance the oil recovery for foamy oil reservoirs after primary production. In the process of CAMF, naphtha can improve the mobility of heavy oil, reduce the resistance to the subsequently injected foaming liquid and methane gas when entering deep reservoir, and create conditions for the subsequent formation of secondary foamy oil. The formation of the secondary foamy oil can reduce the injected gas channeling velocity, improve the elastic energy, reduce the viscosity and interfacial tension of heavy oil, and have certain emulsification effects. For this method, the optimal injection timing occurs when the reservoir pressure drops between the bubble point pressure and the pseudo-bubble point pressure. Simultaneous injection of methane gas and foaming liquid is obviously better than alternating injection. if economic conditions permit, a higher surfactant concentration should be used for CAMF, and the optimum gas-liquid ratio for CAMF is 1:1 under the experimental conditions.