The fitting between the existing impedance modeling analysis results and the actual curve is difficult to meet the working needs of the hybrid power supply system. Therefore, the impedance modeling analysis of the hybrid power supply system of transformer and diesel generator is proposed. The working characteristics of major power generation equipment such as transformer and diesel generator are analyzed and the working principle of the hybrid power supply system is discussed. In consideration of the process of coordinate rotation transformation, port impedance and constant power load, the impedance model of the hybrid power supply system of transformer and diesel generator is established. The power system impedance is measured online, the control parameters of phase locked loop (PLL) are adjusted, and the impedance of the model under the Nyquist curve is output. The test results of the model show that using the proposed method, the degress of fitting of the impedance properties are increased by 20% and 30%, respectively, for the positive order impedance, and increased by 11% and 13%, respectively, for the negative order impedance.