Abstract: Aiming at the problem of low signal-to-noise ratio of electromagnetic ultrasonic signals, the relative nonlinear coefficient is used to predict the tensile strength, and the stress triaxiality is introduced to improve the accuracy of the prediction. A three-dimensional finite element simulation model for the electromagnetic ultrasonic nonlinear detection of plastic damaged specimens is established. Two characteristic parameters:stress triaxiality and relative nonlinear coefficients are calculated. The simulation analysis results show that the sensitivities of the two characteristic parameters to different damage stages are different. The stress triaxiality is more sensitive to the late stages of plastic damage, while the relative nonlinear coefficient is more sensitive to the early damage. An experimental platform for electromagnetic ultrasonic non-linear detection of plastic damaged specimens is established, and the electromagnetic ultrasonic detection of different plastic damaged specimens is performed. The relation of tensile strength with relative nonlinear coefficient and the relation of tensile strength with stress triaxiality for different plastic damaged specimens are further quantified. According to the sensitivity of the characteristic parameters to damage, the combination of the two characteristic parameters can improve the prediction accuracy in predicting tensile strength.