Abstract: The geometric configurations of serpentine nozzles differ significantly from conventional axisymmetric nozzles, characterized by substantial variations in the wall curvature and an S-shaped centerline. This configuration results in uneven distribution of internal aerodynamic load. Serpentine nozzles are generally thin-walled structures to reduce aircraft’s weight. Consequently, the fluid-structural interaction (FSI) becomes a prominent phenomenon in serpentine nozzles, playing an important role in aircraft design. To examine the FSI phenomenon in serpentine nozzles and its impact on thrust performance, this paper introduces double serpentine nozzles with varying offset ratios. A two-way FSI framework is then established and validated. Subsequent analysis focuses on the deformation characteristics of the nozzle and their effects on the aerodynamic loads on the nozzle wall. Furthermore, the influence of FSI on thrust performance is explored. The results reveal that the FSI phenomenon is evident under different offset ratios. There are two types of nozzle deformation: inward-outward and top-down, with the deformation decreasing gradually with the increase of offset ratio. Notably, the maximum deformation consistently occurs at the middle of the lower wall of the nozzle outlet. Regarding the aerodynamic performance, the nozzle's cross-sectional area expands, transitioning from an initial convergence configuration to a convergence-expansion one. Both the throat area and offset ratio decrease approximately linearly with the increase of the offset ratio. The FSI causes the local high-speed flow region at the junction of the second inflection and the outlet to expand and move downstream, leading to a reduction or even elimination of the downstream pressure peak. In terms of thrust performance, the thrust coefficient increases while the thrust vector angle decreases, but the variation trend of both with the offset ratio is consistent with that under uncoupled conditions, and both decrease gradually with increasing offset ratio.