Abstract: The interface pressure between the cable accessories and the cable insulators plays a decisive role in the insulation characteristics of the accessories and the long-term reliable operation of the cable. Considering the actual rough contact interface between the cable body and accessories, a finite element simulation rough contact model of stress field-sound field coupling is constructed by using points with Gaussian probability distribution, based on this model, firstly, the differences of echo signals in time domain and frequency domain at different positions of cable accessories, and the differences in time domain and frequency domain under different interface pressures at the same position are analyzed. Secondly, the functional relationship between interface pressure and nonlinear parameters is fitted. Finally, the nonlinear ultrasonic test platform is built to measure the interface pressure at different positions of the cable intermediate joint to verify the accuracy of the relationship between the interface pressure and the nonlinear parameter function. The test and simulation results show the same regularity in the time domain and frequency domain of the echo signal, and the nonlinear parameters increase with the increase of interface pressure. The test results show that the value of the detected nonlinear parameter is around 7.46×10⁻³ (the error range is within 5.80%), which corresponds to the interfacial pressure of 0.21 MPa; and the value of the detected nonlinear parameter is around 6.38×10⁻³ (the error range is within 7.60%), which corresponds to the interfacial pressure of 0.16 MPa. The nonlinear parameter can characterize the size of the interfacial pressure in different locations, and it is possible to characterize the size of the interfacial pressure at different locations. It verifies the validity of the simulation fitting function relationship and provides a new idea for measuring the interfacial pressure of cable accessories.