The research on the correlation between pollutant dispersion and wind environment is gaining more and more attention due to increasingly serious air pollution. However, the specific relationship between wind environment factors and the pollutant concentration is still unclear. In this paper, a simple model of the relationship among wind speed, pollutant concentration, and pollutant dispersion efficiency is investigated based on computational fluid dynamics (CFD) simulations to redefine the static wind speed on the aspect of pollutant dispersion. The air pollutants are supposed to be diffused effectively when the wind speed is higher than the static wind speed. The CFD simulations are performed using the three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) methods. First, the numerical methods and CFD settings are described briefly and then validated by experimental data. Next, an idealized pollutant dispersion model is established and then the pollutant dispersion processes are simulated and analyzed with different wind speed profiles. Finally, wind with speed less than 1.0 m/s at pedestrian level (1.5 m above the ground) is defined as static wind according to the comparison and analysis. It is expected that the static wind speed results can be easily used as an indicator to evaluate air quality directly for urban design and planning.