Abstract: To further understand the effect of wind direction on the aerodynamic forces and flow fields of two tandem tapered square cylinders, three-dimensional (3D) large eddy simulations (LESs) of the flow around the two cylinders with a spacing ratio G/D = 4 (G is the cylinder center-to-center distance and D is the cylinder width) are conducted at Reynolds number (Re) = 2×10³. The influence of the wind directions (α = 0°~45°) and tapered modifications (ξ = 0% and 5%) on flow regime, aerodynamic force coefficient and wind pressure distribution are comprehensively analyzed. The flow field is also investigated to reveal the variation and interference mechanism of the aerodynamic forces, then the mathematical relationship between the wind directions and the aerodynamic force coefficients is established. The results indicate that the flow structures can be divided into three flow regimes based on the wind direction: leading-edge separation (α = 0°), separation-bubble (α = 5°, 10°, and 15°) and attached-flow (α = 30° and 45°) regimes. There is an abrupt change in the mean and fluctuating force coefficients, as well as vortex shedding frequency of the two cylinders when the flow regime is transformed. The maximums of the fluctuating force coefficients and the vortex shedding intensity occur at α = 5°, while the vortex shedding frequency is the smallest. The shear layer and the wake vortex reattach on the surface of the downstream cylinder when the flow structures are in the leading-edge separation flow regime. The flow structures exhibit a skew feature in the attached-flow regime, which resulting in the variation in the aerodynamic forces with the wind direction. Meanwhile, the mean and fluctuating force coefficients, wind pressure coefficients, and vortex shedding intensity all decrease with the increase in taper ratio, however the vortex shedding frequency increases. It may be attributed to the narrower shear layer and the weaker periodicity and consistency of the vortex shedding.