Abstract: For the noise contained in the flow-excited response signal of high arch dams, it is easy to cause the distortion problem of the operation mode identification of discharge structure.A mode parameter identification method of high arch dams subjected to flow excitation based on masking signal processing technique is proposed.In view of the fact that measured response signals of a high arch dam flow discharge vibration are easy to be submerged by noise and difficult to extract, we analyze the mechanism of a high arch dam structural mode confusion, and then add artificial masking signal to the bandwidth signal in the response sequence that may cause structural mode distortion, so as to increase the frequency saliency of the signal sequence.Based on this, a complete ensemble empirical mode decomposition with adaptive noise method is constructed, which is suitable for decomposing the vibration response signal of closely spaced modes structure, and then the Hilbert-Huang transform and random decrement technique are used in combination to identify the operating mode of a high arch dam.Engineering example shows that the established method can effectively inhibit the mode confusion in structural parameter identification of high arch dams, while avoid the loss of mode information and improve the accuracy of parameter identification.