At present, studies on the mechanical properties of unicuspid aortic valve (UAV) were rare as most of the research works were focused on the statistical analysis of related diseases in patients. A 3D fluid-structure interaction model based on the arbitrary Lagrangian-Eulerian method was established by utilizing the COMSOL finite element software and the hemodynamic characteristics of UAV throughout the systolic period under different conditions were analyzed. Firstly, the effectiveness of the proposed model and algorithm was verified by simulating the Poiseuille flow and the flow-induced vibration of an elastic beam behind a cylinder. Then, fluid-structure interaction simulation was performed for UAV problems and its mechanical properties were analyzed. The results show that UAV is narrower and has higher transvalvular pressure gradients and fluid shear stress when compared to the normal aortic valve; under the condition of low blood flow, UAV is narrow and has a low blood flow velocity and low transvalvular pressure gradients; the aggravation of calcification can make UAV narrow again, which forms a vicious cycle.