The fluid excitation source of centrifugal fan is located in the fan， and it is a distributed excitation source. The distribution of the excitation force is calculated by computational fluid dynamics （CFD） analysis， but it is not able to calculate the excitation force through the dynamic response of the surface to verify the correctness of the CFD results. The identification model of the equivalent excitation source is established. The vibration of the volute and the transfer function from the candidate equivalent excitation point to the vibration measurement point of the volute are obtained by experiments. The pressure fluctuation of the centrifugal fan operating at the ratings is measured. The pressure fluctuation distribution on the volute surface is obtained by polynomial fitting， which provides the basis for the selection of the equivalent source. The minimum error algorithm is used to optimize the selection of equivalent excitation source candidate points and inversion measurement points， and the equivalent excitation force is obtained by Tikhonov regularization algorithm inversion. Then the measured transfer function and the inversion equivalent excitation force are used to calculate the vibration response of the volute and motor mount， to verify the equivalence and accuracy of inversion results. The error between the inversion result and the measurement result at blade passing frequency is about 2 dB， and the equivalent excitation force inside the centrifugal fan is successfully inverted.