The invention belongs to the technical field of tertiary oil recovery and particularly relates to a method for extracting oil in single well steam stimulation by combining microorganisms and CO2 in the heavy oil well. The method comprises the following steps: (1) screening test oil wells; (2) screening microorganisms and nutrients thereof; (3) injecting the microorganisms and the nutrients thereof into the stratum of the test oil well; (4) injecting liquid CO2; (5) shutting the test oil well down; (6) opening the test oil well for production. The method disclosed by the invention has the advantage of wide application range and is simple in process implementation; oil well sand production and sleeve damage situations are avoided and the oil well utilization rate is high; the thickened oil viscosity can be greatly reduced, the oil-water interfacial tension is reduced, the stratum energy can be effectively replenished, the characteristics of long action period, remarkable enhanced production effect of oil, and the like are achieved, and therefore, the method is an economic and effective method for increasing the yield of the heavy oil well and can be widely applied to a single well steam stimulation technology of the heavy oil well.