An equivalent linear model for the seismic analysis of the isolated gas duct using thermal sliding double concave friction pendulum(TS-DCFP)system is established. The structure is modeled as a two-degree-of-freedom system in the transverse direction. Meanwhile, the effective stiffness and equivalent viscous damping ratio of an isolation bearing with tri-linear behavior are derived and the modal-combined damping ratio is obtained from the modal potential energy ratio of components. The model is verified by comparing the response of a linear time history analysis of the two-degree-of-freedom system with that from the 3D nonlinear time history analysis using the directly integrating method.