Abstract: The valuable application of detecting fatal defects in forging parts by using bottomed-echo method was explored. According to bottom-echo method theory, analysis of several factors causing attenuation of back-echo showed that the defect nature was the primary factor of attenuation under certain conditions, and application scope of the method was discussed.Based on these, bottom-echo method was proposed to use other assisted detection technology for the evaluation of defect nature and work piece quality applied in practice, the effect was good.