Based on the two-dimensional Reynolds averaged SST k-ω and the three-dimensional large eddy simulation LES model,the vortex-induced vibration of a rectangular cylinder with an aspect ratio of 1∶4 was numerically simulated. The mechanism of vortex-induced vibration was compared and analyzed from the energy and perspective of the flow field. Through the numerical simulation method combined with the dynamic grid technology,the vibration response of the rectangular cylinder is solved by compiling and embedding UDF into Fluent,which is compared and analyzed with the wind tunnel test results. Besides,the difference between two-dimensional and three-dimensional numerical simulation results is explained from the energy and perspective of the flow field. The results show that the numerical simulation methods of two-dimensional and three-dimensional models can accurately capture the vortex-induced vibration range of a rectangular cylinder. The three-dimensional model can accurately capture the vortex vibration amplitude,but the amplitude of the two-dimensional model is too large. Due to the different vortex sizes,structural forms,and phases of the three-dimensional rectangular cylinder model,the lift of the three-dimensional model is less than that of the two-dimensional model as a whole. The root means the square of the pressure coefficient of the two-dimensional model is greater than that of the three-dimensional model as a whole. Therefore,the input energy of the two-dimensional model is greater than that of the three-dimensional model,resulting in a large amplitude of the two-dimensional model. The research findings can offer insights into the numerical calculation of vortex-induced vibration of bridge sections.