Abstract: This paper discussed the rationale of impact-echo method with the theory of wave propagation.By means of testing the concrete model and the highway concrete model, we studied the variations of the peak frequency and thickness-testing results at different impacts.The result proves that applied effect of impact-echo method is of much limit on the condition of ordinary impact ways.Otherwise,the impact ways and test object are important influence of the result.We also discussed the development tendency to this method and its limitation.