The invention relates to an impedance matching method of a plasma etching system. The impedance method comprises the steps of providing a plasma etching system, wherein the plasma etching system comprises an impedance matching device, the input end of the impedance matching device is electrically connected with a source power and a bias power supply, the output end of the impedance matching device is electrically connected with a reaction cavity, the end, connected with the source power, of the impedance matching device is electrically connected with one end of a voltage-current detector, and the other end of the voltage-current detector is connected with the source power through a frequency regulation control unit; the source power and the bias power supply simultaneously work under a continuous power mode, and a first matching frequency can be obtained by adjusting the frequency of the source power; the bias power supply is converted into a pulse power mode, and the first matching frequency serves as a benchmark frequency of the source power under a bias power supply pulse opening state, and when the bias power supply is converted to a pulse closing state from the pulse opening state, the benchmark frequency is adopted as the benchmark, so that a second matching frequency can be obtained by increasing or reducing the frequency of the source power.