Abstract: The use of expansion compensation device (OFFSET) in bridge-along cable is to offset the impact of bridge displacement on the stability of the cable structure. The real-time compensating performance of the OFFSET device is crucial for the safe operation of bridge-along cable. Therefore, taking a prototype OFFSET device on a certain sea-crossing bridge as the research object, we established a rigid-flexible hybrid multi-body dynamics model, and simulated the compensating performance of the OFFSET device under displacement load and displacement-current load. Then, the displacement response of the clamp was calculated as the boundary, and the mechanical response of the cable was obtained by the finite element simulation of the electric-thermal-structural coupling model. The validity of the established model was verified by comparing the numerical simulation results with the results of prototype test of OFFSET device. The results show that the OFFSET device can achieve the designed compensation performance, and the maximum stress distribution of the bridge-along cable is located at the fixed clamp. Under the combined action of displacement caused by daily ambient temperature and the load current, the maximum stresses on the conductor and aluminum sheath are 84 MPa and 155 MPa, respectively, and the minimum stresses are 55 MPa and 105 MPa, respectively. The maximum strain of aluminium sheath is 14 881×10⁻⁶, and the minimum strain is 9340×10⁻⁶. The maximum axial force of the clamp is 7.4 kN, and the minimum axial force is 4.8 kN. The stress on the metal layer of the cable, the strain of the metal sheath and the axial force on the clamp will change in a sine law. The research results provide a methodology and basis for the real-time compensation performance of the OFFSET device and the status evaluation of bridge-along cable.