Objective To study the mechanical properties and changes in the carotid vessels of cystic tumors during periodic blood flow to explore the specific mechanism of the development of cystic tumors and the effects of tumors on blood flow. Methods Finite element numerical simulation of the interaction between cystic tumors and blood in the carotid artery was conducted using a two-way fluid-structure coupling method. The deformation of blood vessels, blood velocity, mechanical properties in key areas, and influence of the tumor on blood vessels were analyzed. Results At the boundary between the tumor and blood vessels, the tumor showed a large deformation and low pressure on the tumor wall. The pressure on the opposite vascular wall and triangular area around the vascular bifurcation of the tumor was high, and it could easily stretch or rupture. The blood velocity inside the tumor was lower than that in normal blood vessels, indicating that the internal space of the tumor was not fully utilized. The wall shear force on the tumor during the pulsation period was always small, which lead to the deposition of impurities that form atherosclerotic plaque. Conclusions Cystic tumors interfered with normal blood flow in the blood vessels and promoted the production of mirror tumors. This study provides a theoretical reference for the treatment and prevention of cystic tumors. By understanding the mechanical properties of cystic tumors and their effects on blood vessels, doctors can develop personalized treatment plans and improve treatment outcomes.