The invention belongs to the field of aero-engines, and particularly relates to an aero-engine modeling method with a CDFS structure. The method comprises the steps of 1, constructing a numerical model of the CDFS; 2, a numerical model of a front duct ejector is constructed according to the numerical model of the CDFS, and the front duct ejector is used for controlling the outlet area of the firstouter duct and the outlet area of the front mixing chamber; Step 3, constructing a balance equation when the selection valve is opened and closed; wherein when the selection valve is opened, a frontmixing chamber inlet airflow static pressure balance equation and a front mixing chamber airflow total pressure balance equation considering the volume effect are constructed, and opening and closingof the selection valve correspond to opening and closing of an inlet of the second outer culvert respectively. According to the invention, the numerical model of the CDFS and the numerical model of the CDFS post-deflation duct are constructed, and the real-time mixing condition of the multiple air flows of the aero-engine with the CDFS structure is calculated, so that the purpose of real-time numerical simulation is achieved.