The invention discloses a large-area structural damage detection method based on a Lamb wave. The large-area structural damage detection method based on the Lamb wave comprises the following steps: arranging a Lamb wave exciting device on a to-be-detected point of a to-be-detected structure; exciting a narrow band signal by a function generator and a power amplifier, controlling the band width range of the narrow band signal to be at the frequency band lower than the set A1 mode cut-off frequency, loading the excited narrow band signal to a mobile probe, generating a single A0 mode Lamb wave the frequency value of which is less than the A1 mode cut-off frequency on the to-be-detected structure, and receiving the Lamb wave signal by the mobile probe so as to acquire a Lamb wave echo signal f containing the damage structual information; collecting signals on residual to-be-detected points on the to-be-detected structure sequentially according to the mode, and collecting the response signal fm of the single A0 mode structure; and carrying out signal processing on the collected response signal fm to obtain a damage image, positioning the position of the damage of the to-be-detected structure, and estimating the damage situation of the structure.