Abstract: The interface pressure between a cable and its accessories plays a decisive role in the long-term stable operation of the cable. The pressure sensor measurement method can damage the interface insulation characteristics, thus a non-destructive testing method based on ultrasonic non-linear effects was proposed. Firstly, the propagation characteristics of ultrasonic waves at the silicone rubber-cross-linked polyethylene interface were analyzed. The relationship between the non-linear coefficient and the interfacial pressure was obtained. Then a non-linear ultrasonic test platform was built based on the pulse reflection method. Moreover, the interface pressure of flat silicone rubber and cross-linked polyethylene was examined by non-linear ultrasonic testing. Both theoretical and experimental results show that, as the interface pressure increases, the interface primary echo amplitude decreases, the echo time decreases, and the non-linear coefficient increases. The results show that non-linear ultrasound can effectively evaluate the interfacial pressure state of cable silicone rubber composite, which can provide strong support for the subsequent interfacial pressure detection of the curved structure of cable accessories.