Hitherto, research on the fluid-structure coupling of coronary stents has mostly considered the state after stent expansion following implantation. However, the factors and how they affect stent expansion are as yet, unclear. To further investigate stent expansion, this paper proposes a model combining balloon, stent, and blood using Solidworks. Thereafter, a co-simulation using ANSYS Workbench is implemented using the methods of finite element and finite volume, to analyze bidirectional fluid-structure coupling during the expansion of a balloon-expandable stent, for periodically varying blood loads. By comparing the blood flow rate in the vessel, pressure on the endovascular wall, and the pressure and stress on the stent system at different points in time, it can be seen that the higher the blood flow rate, the greater the pressure on the endovascular wall and stent system. Furthermore, the larger the volume of the implant, the greater the maximum blood flow rate and maximum pressure on the endovascular wall, and the more drastic the change along the axis. In summary, the results of the present study indicate that the stent expansion process has a significant effect on the blood flow rate and pressure on the vascular wall; however, the impact of blood load on stent stress can be ignored.