Abstract: A concrete stress detection method based on nonlinear ultrasonic harmonic effects was proposed in this paper. Since the linear ultrasonic method is not sensitive to early stress of concrete and the nonlinear ultrasonic harmonic method can better reflect the characteristics of material cracks and stress evolutions. First, a constitutive model for the axial stress of concrete and its acoustic parameters of nonlinear response were established by using the relationship between the crack evolution of concrete material and the nonlinear second-harmonic effect of ultrasonic waves. Then the main influencing parameters of this method were clarified. Lastly, the ultrasonic harmonic stress detection tests for concrete standard specimens were carried out and a comparative analysis with the textual model was made to verify the effectiveness of the proposed detection method. The results may provide a reference for concrete stress detection in engineering.