This study was focused on damage monitoring and estimation of 16Mn steel structures. This study used acoustic emission (AE) cusp catastrophe model to estimate the time at which the state of 16Mn steel will change from elastic deformation to yield deformation. Firstly, the tensile test of 16Mn steel plate specimens was monitored with acoustic emission technique. Secondly, a acoustic emission cusp catastrophe model was establish based on cusp catastrophe theory and acoustic emission signals. Finally, some catastrophe time was estimated with AE cusp catastrophe model. At this catastrophe time, the state of 16Mn steel plate specimen might change from elastic deformation to yield deformation. The experimental results show that AE cusp catastrophe model can estimate the time at which the state might change from elastic deformation to yield deformation of 16Mn steel in tensile test.