With exacerbating air quality due to pollutant emissions and rising energy supply crisis, the wind energy consumption will play a key role in future energy structure in China. To utilize the wind energy optimally, a better understanding and quantification of wind resource such as the temporal-spatial and vertical distributions is vital prior to exploitation. Based on wind measurements from 1991 to 2011 on a 15-level 325 m meteorological tower in Beijing, we assessed the potential of wind resource using the Weibull function and the wind atlas analysis and application program (WAsP) software. Results show that wind resource has significant seasonal and diurnal variations and diurnal variation varies with height. Additionally, although the wind resource increases with height, there is a strong wind shear layer related to the complex urban underlying surface. Furthermore, observation and WAsP simulation show that larger wind resource mainly comes from northwest wind in northwestern or northern Beijing. However, considering the regional average wind resource, we concluded that wind resource in Beijing is suitable for small wind turbines, yet the decreasing trends of wind resources seem to make wind energy unsustainable.