In order to understand the flow characteristics around the square column with a finite length and determine end effects on the distribution of aerodynamic forces, research work was conducted based on numerical simulations, and the corresponding phenomenon was explained according to the change in flow field. Firstly, taking the two-dimensional square cross-section as the object, the reliability of the numerical model and method was verified without considering the end flow, and the influence of aspect ratio on aerodynamic characteristics of the cross-section was also discussed. Then, taking the three-dimensional square column with a finite length as the object, the evolution law of aerodynamic force distribution with spanwise length was identified, and the influence range of end flow was determined. The results show that the vortex length in the wake region increases while the negative pressure region decreases with the increase in cross-sectional aspect, resulting in a linear decreasing trend for the drag coefficient and Strouhal number. When the ratio of length to height is less than 20, the entire drag coefficient and Strouhal number for the square column increase rapidly with the increase in spanwise length. The wake field changes greatly, exhibiting significant three-dimensional characteristics. With the further increase in the ratio of length to height, the entire drag coefficient and Strouhal number continue to increase with slower amplifications. However, the end flow still has significant effects on the wake field. The vortex shedding phenomenon weakens at two sides of the square column, so the aerodynamic force exhibits a distribution of larger values in the middle and smaller values at the sides.