The purpose of this paper is to investigate the effect of aspect ratio on vortex on vortex shedding and transient flow induced noise over a rectangular cylinder is presented. The freestream velocity is assumed 50 m/s. URANS equations with turbulence model k-ω-SST are employed to flow analysis. Aerodynamic noise calculations are performed using FW-H analogy. The rectangular cross-section with various lengths and widths is considered. Comparison of the results extracted in the present study with the experimental results of other reference indicates the accuracy of the present research. In this study, the aspect ratios from 0.6 to 6 (equivalent to Reynolds numbers from 2.5×10^4 to 5.6×10^4) is studied. The simulations can be divided into two categories. In the first category, the ratio of length to width (R=B/H) is less than one, and in the second one, this ratio is greater than one. In the first case, noise is reduced by a relatively low slope. But in the second condition, the behavior of noise is different in various ratios and the slope of noise variations is high. The flow structure is also discussed in this paper. It is founded that for the first category, by increasing aspect ratio both the fluctuations and aerodynamic forces are reduced and the longitudinal wake zone is increased. But in the second category, fluctuations of flow may be increased or decreased in various aspect ratios.