On international thermal nuclear experimental reactor (ITER) superconducting fusion device, Nb3Sn composite strands have been applied to CICC (cable-in-conduit conductor) to undergo the impact of the magnet field above 12 T. The strain of Nb3Sn-based conductor due to Lorentz forces leads to changes in critical current and coupling loss time constant. Therefore the study on the critical performance degradation of CICC is still inadequate, and the influence of the contact properties with strain on the coupling loss time constant is also insufficient. In order to calculate the coupling loss accurately and quickly, a new calculation model of coupling loss time constant was put forward in this paper. The model is expressed by a linear equation using some parameters such as the cabling sequence ratio, contact resistance and void fraction with strain main from electromagnetic force. In this model, the computation expression of cabling sequence ratio, as well as the contact resistance and the void fraction are obtained under the strain from cyclic electromagnetic load. Compared with numerical calculation using Gandalf and the traditional method, coupling loss calculated by the new model has a small error, and it is close to the engineering measurement.