The invention belongs to the technical field of high-frequency transformer modeling and particularly relates to a method for extracting the parasitic capacitance of cascaded isolation transformers. The method comprises steps of constructing a single isolation transformer equivalent circuit model based on the low-frequency magnetic effect and the high-frequency capacitance effect of the isolation transformer; enabling a model of n cascaded isolation transformers to be equivalent to a chain circuit to calculate a cascaded isolation transformer port impedance function; constructing a relational expression between a cascaded isolation transformer port impedance resonant frequency and a circuit parameter according to pole-zero analysis; testing, by an impedance analyzer, the port open-circuit impedance resonant frequency of the cascaded isolation transformers, and the low-frequency input-end impedance of the cascaded isolation transformers when the output end of the cascaded isolation transformers is in an open-circuit state and a short-circuit state, calculating the excitation inductance and the leakage inductance, and calculating the parasitic capacitance of the isolation transformers. The method can conveniently and effectively extract the parasitic capacitance in the transformers without internal structure data, and helps to study the broadband characteristics and the parasiticparameter effect of a cascaded transformer two-port network.