In order to apply the biogeography-based optimization ( BBO) algorithm to the structural damage detection, the algorithm is improved with the cosine migration model, the adaptive immigration function and the elitist mechanism. With the example of a simply supported beam under different damage situations, BBO algorithm is applied to detect not only the damage position but also the damage degree. The result indicates that compared with previous BBO algorithm, the improved one has the advantage of easier calculation, faster convergence speed, higher identification precision, and better stability, thus it can be effectively applied to the structural damage detection.