Abstract: The damage thresholds obtained by natural frequency method can be usedas a criterion to justify theusefulness of practical engineering structure. The natural frequency methodconsists of analyzing the influential factors of the damage, and acantilever beam model is taken as an example. Both numerical and theoretical results indicate that, if thefrequency measurement error is known, this method can be used toestimate the thresholds, during the early periodof damage. The thresholds obtained by this method agree with the numerical resultsvery well.