The invention discloses a foam flooding method for thickened oil, and belongs to the technical field of thickened oil recovery. The method comprises the following steps: a foaming system is injected into the bottom of a gas injection well, wherein the gas-liquid ratio in the foaming system ranges from 1 : 1 to 1.5 : 1, and the foaming system comprises air and a foaming agent of which the effective concentration is larger than or equal to 0.06%; the foaming system forms foam at the well bottom; the foam enters oil layer pore space and seeps. According to the invention, through the utilization of the principle that foam still has higher viscosity which is far higher than the viscosity of raw oil under the stratum condition after encountering oil and being shattered, an oil displacement system has the function of fluidity control after entering a target oil layer, the problem of gas channeling of the oil displacement can be solved; meanwhile, through the adoption of the thickened oil foam flooding, the function of improved sweep efficiency of the oil layer can be met, and further, the recovery efficiency of the thickened oil is improved; in addition, fuel gas is controlled out of the explosion range, or the oxygen content is controlled lower than the minimum value of critical oxygen content, namely safe oxygen content, so as to prevent explosion.