A CO2 flooding foam oil stream component determining method, and a CO2 flooding simulation method are provided; the CO2 flooding foam oil stream component content determining method comprises the following steps: a parameter determining step, determining the thermodynamics parameter, relative permeability and each component of the foam oil stream, and a bubble mol percentage; a component determining step, determining each component and bubble contents according to the parameters obtained in the previous step and a preset component model. The CO2 flooding foam oil stream component determining method uses the preset component model of foam oil stream in a CO2 injection process to accurately simulate the foam oil stream distribution and dynamic characteristic simulation in the gas injection process.