This paper proposes a new measurement metric for estimating the defects in a metal pole by analyzing its hammering sounds. The validity of this measurement metric is supported by the simulation which is based on the Stress Harmonic Analysis. Moreover, the simulator is constructed by applying Model Based Approach and this makes it possible to extend the simulator to be applicable to some variations of metal poles. The configuration of the defect estimation system, the proposed measurement metric and the details of Stress Harmonic Analysis are described. As a result, the possibility of applying the proposed new measurement metric is increased in the actual defect estimation of metal poles.