In this paper, a new concept of combination degree (CBD) is proposed. And the CBD between nylon and insert in the pipe wrench is investigated using ANSYS .Then studied the effects of factors on the CBD, such as load, elastic modulus, friction coefficient and behavior of contact surface between the nylon and the steel insert. The results indicate that as the load increases from500Nm to1500Nm, the CBD declines from4.92mm-1 to 1.23mm-1, which presents the combinative characteristics become worse. However, with the elastic modulus and the friction coefficient increases respectively, the CBD also increases. When the elastic modulus is 8000MPa, its CBD goes up to1.78mm-1. As the friction coefficient ranges from 0.1 to 0.5,the CBD increases from1.56mm-1 to 2.32mm-1.In addition, different behaviors of contact surface between the nylon and the insert have different effects on the CBD. When such behavior of contact surface is bonded, its CBD is the highest, 3.31mm-1, but when such behavior of contact surface is standard which means that if the separation between the nylon and the insert occurs, the normal pressure equals zero. And its CBD is the lowest, 1.78 mm-1.