Abstract: The aerodynamic forces on a wall-mounted finite-length square cylinder with one end mounted on a wall and the other end free are experimentally investigated.The width of the test model is d =200mm,and the aspect ratio is H/d =5.The incoming flow velocity is U ∞ =13m/s,corresponding to a Reynolds number of 1.73×10 5 based onU ∞ and d .It is found that the time-averaged drag coefficient CD and rms value of the lift coefficient C′L of a 3D square cylinder are both significantly smaller than those of a 2D square cylinder,and the vortex shedding fre-quency of the former is lower.Two typical flow modes occur in the flow around a 3D square cyl-inder:the first mode is characterized by alternating spanwise vortices shedding,similar to Kar-man vortex street,corresponding to higher drag and larger fluctuation of lift;the second mode is characterized by symmetrical vortex shedding,corresponding to lower drag and the lift without periodic fluctuation.At the lower part of the cylinder,C′L of the first mode is about one times lar-ger than that of the second mode,and this difference reduces gradually as approaching the free end.Besides,the spanwise correlation of the aerodynamic force is stronger in the first mode. These two typical flow modes occur randomly,resulting in the nonstationary properties of the aerodynamic forces on the wall-mounted finite-length square cylinder.