The influence of the aspect ratio on two-way fluid-structure interaction characteristics of double serpentine nozzles for turbofan engines was investigated by the serial two-way loosely coupled algorithm. The results show that the structural displacement characteristics of the serpentine nozzle are mainly located in the downstream channel of the first bend and the exit upper wall of the equivalent section of the nozzle， and that with the increase of the aspect ratio， the displacement of the downstream area of the first bend of the nozzle gradually increases， while that of the exit of the nozzle first increases and then decreases. The maximum displacements of the upper and lower walls of the serpentine nozzle both appear in the downstream wall of the first bend. Because of the outward expansion of the nozzle outlet wall， the outlet aspect ratio decreases compared with the design value under fluid-structure interaction. The fluid-structure interaction influences the flow field characteristics and flow losses of different aspect ratios. The flow vortex caused by the deformation of the nozzle structure has a large influence on the downstream flow of the nozzle with a small aspect ratio. In this case， the axial bending angle of the nozzle decreases and the thrust vector angle decreases. In the case of large aspect ratios， the nozzle axial bending angle increases with the increase of the aspect ratio， and the thrust vector angle increases. At an aspect ratio of 2， the total pressure recovery coefficient is reduced by 0.56%， the flow coefficient 2.67% and the thrust coefficient 0.72%， while the three are reduced by 0.36%， 4.34% and 1.37%， respectively， when the aspect ratio is 10.