The invention discloses a supercritical CO2 microemulsion formed by an anionic-nonionic amphoteric surfactant. 100 parts by weight of the supercritical CO2 microemulsion are prepared from the following components: 0.1-20 parts of water, 1*10<-4>-1*10<-1> parts of the surfactant, 1-10 parts of a cosolvent and the balance of CO2. The preparation method of the supercritical CO2 microemulsion comprises steps as follows: (1) the cosolvent in certain mass is mixed with water at the temperature of 20-25 DEG C and stirred uniformly; (2) the anionic-nonionic amphoteric surfactant in certain mass is weighed and added to a mixed solution of the water and the cosolvent and stirred to be dissolved; (3) the mixed solution is added to a transparent high-pressure container, CO2 is introduced, the mixture is stirred and completely miscible, and the supercritical CO2 microemulsion is formed. The anionic-nonionic amphoteric surfactant does not have a cloud point and has good solubility, good hydrophilia and a wide application range; ion components are simple, and the interface stability is high; polar heads are distributed more uniformly in a concentrated manner through the single-stranded surfactant, and the hydrophilia is higher; the surfactant has high solulbilizing power and is low in cost and suitable for large-scale application in an oil field.