The invention discloses a Lamb wave structure-based multi-mode signal separation method. One or more modes are extracted from a multi-mode Lamb wave signal according to the wave structure features of different modes of Lamb wave; each mode-information in the multi-mode Lamb wave signal can be quantitatively analyzed; the method can be used for researching the phenomena such as reflection, transmission and mode conversion of each mode of Lamb wave at the discontinuous position of the structure and can also be used for researching the problem of the amplitude value of an excitation signal of each mode of Lamb signal under different excitation conditions.