Abstract: As a new type of ultrasonic testing method, the nonlinear ultrasonic testing technology has attracted wide attention due to its high detection performance for small defects and no influence of material shape in the testing process. Based on the domestic and foreign research results, this paper introduces the principles, application and advantages of the high-order harmonic method and several mixing methods, summarizes the current situation of nonlinear testing technology and puts forward the prospect for the future development.