Taking metallic cantilever beam as the research subject, using fiber Bragg grating strain sensing array as the detecting means, a new method is studied to detect multi-crack damage of cantilever beam. First, the strain test method of fiber Bragg grating sensing array is studied. Damage of cantilever beam has been prefabricated by using the wire-cutting technology. When the cantilever beam is not damaged, the wavelengths of fiber Bragg grating are changed by adding the weight, then the changes of fiber Bragg grating wavelength are acquired, and the changes are taken as the initial data. When one crack is prefabricated on the cantilever beam, using the foregoing method, the wavelengths of fiber Bragg grating are changed by adding a weight. The changes of fiber Bragg grating wavelength are acquired. The first group of damage data is obtained. Accordingly, the second crack and the third crack are prefabricated in the cantilever beam. Using the foregoing method, the other two groups of damage data are acquired. So three groups of damage data are obtained, then comparing the three groups of damage data with the undamaged data, and the damage recognition of cantilever beam is realized. The experimental result indicates that fiber Bragg grating strain sensing array can exactly and sensitively detect damage information of cantilever beam. It is a new sensing method in damage recognition field.