Abstract: Two deficiencies of the curvature modal difference (CMD) index are firstly proved through theoretical analysis. One is that the CMD index is insensitive to damages occurring at curvature modal nodes and another is that the CMD could not reflect damage degree effectively. Then a new improved index called superimposed curvature modal change rate (SCMCR) is proposed in this paper, which can overcome the deficiencies of the CMD index theoretically. A continuous beam is selected as a numerical example and the results show that the SCMCR index could reflect both the location and degree of damage | it is superior to the CMD index. Finally, a method for estimating damage factors based on the new index is proposed and validated.