In this paper, the coupling response of incomplete shielded cable under external electromagnetic field is studied. The unbalance difference theory is used to analyze the discontinuous structure of the incomplete shielded cable, and the field-line coupling model of the incomplete shielded cable based on the discretization Baum-Liu-Tesche (BLT) equation is established. At the same time, a test platform for field - line coupling of incomplete shielded cable is established. Based on theoretical modeling and experimental testing, some regularities of the line coupling response of the incomplete shielded wire field are obtained, which have certain guiding value for measuring the electromagnetic compatibility performance of the terminal equipment with incomplete shielded wire.