Abstract: To make full use of the locally enhanced wind around buildings, an unsteady numerical simulation was conducted on a vertical axis wind turbine in building environment. The flow field around an original three-straight-blade vertical axis wind turbine with NACA0021 airfoil was numerically studied and compared with experimental results, while the features and advantages of a building augmented vertical axis wind turbine in capturing wind energy were investigated considering the altitude supremacy of skyscrapers, the effect of enhanced wind speed by building diffusers and the local wind direction. Results show that the power coefficient of a building augmented vertical axis wind turbine may be promoted up to 2.47 times of the original one, but its load fluctuation is stronger, which places a higher requirement on the safety and reliability of the building, and it is rather sensitive to the wind direction, the arrangement of building diffusers and the building profiles, etc.