In this paper, a sensing simulation method for fiber Bragg grating (FBG)-based mechanical structures, based on Livelink data interaction, is proposed. The proposed simulation method combines the FBG sensing simulation model with the COMSOL finite element multiphysical field coupling model using the Livelink module. An interactive model based on the combination of COMSOL and MATLAB was established to realize the simulation analysis of the FBG sensing signal from mechanical structures under multiple physical fields such as stress and temperature. Moreover, an efficiency optimization module based on an adaptive sliding window was adopted to improve the speed of simulation of the FBG reflectivity spectrum. Finally, a typical H-beam structure and FBG sensors were used to verify the FBG-based mechanical structure sensing simulation model. Results show that the error of the FBG center wavelength offset between simulation and experiment is less than 4.6%, and the root-mean-square error is less than 0.0048. In an impact-loading experiment, simulation results were in good agreement with the measured data, which further verifies the correctness of the simulation method proposed in this paper. Furthermore, this simulation method can lay the foundation for the arrangement of FBG sensor networks.