Abstract: In this paper,nonlinear ultrasonic and acoustic emission detection technology were used to study the damaging progress of T700 carbon fiber composite material under loading and unloading experiments. The evolution of ultrasonic nonlinear coefficients in different loading stages of the specimen was analyzed. Combined with acoustic emission characteristic parameter analysis and Felicity ratio, the correspondence relationship between change curves of Felicity ratio and nonlinear coefficient at different loading stages was verified. The results show that,ultrasonic nonlinear coefficient is highly sensitive to damage of T700 carbon fiber composites, which can reflect the dynamic change law of damage through its time domain experience. And it is in better agreement with Felicity ratio of the acoustic emission. Therefore, the ultrasonic nonlinear coefficient can be used as a new method to evaluate the damage severity in the process of static tensile test.