For real complex structures, model updating by conventional finite ele ment model updating methods is difficult due to the heavy computational burden f or the dynamic analysis. Component mode synthesis (CMS) is an effective techniqu e for the dynamic analysis of complex structures. An updating method based on CM S was proposed to improve the efficiency of model updating of real complex struc tures. A condensed structural model was obtained by the CMS technique, and then an optimal objective function was generated, which consisted of frequencies of t he condensed model and the modal shapes transformed from condensed coordinates t o initial physical coordinates. The updated model was acquired by solving the op timization problem. The proposed method was validated by updating a scaled suspe nder arch bridge model using the dynamic measurement data. The result shows that the proposed method is computationally efficient and yet has a high accuracy.