The purpose of this study was to investigate the effect of a new building which can impose on its immediate ambient environment, on air movement and thermal comfort of people using the area. The effect of eight prevailing wind directions around the building was simulated using computational fluid dynamics (CFD). The CFD simulation was validated by two wind tunnel experiments. The CFD results were used to conduct an air ventilation assessment using velocity ratio (VR) indicator and to assess thermal comfort by an extended predicted mean vote (PMV) evaluation. An analysis of the relationship of VR and PMV with the to-be-built building (the front area index lambda(f) and plan area density lambda(p)) was also conducted. The result indicates that the PMV trend was generally opposite to the VR trend. The lambda(p) would increase due to the new building and the lambda(f) would increase in all wind directions except East-South-East and South-East. There could be a significant change in thermal comfort when the lambda(f) became smaller than 12% and a significant change in ventilation efficiency if the lambda(f) was smaller or larger than 12%. It means that lambda(f) can be used as an urban planning parameter for the thermal comfort study in the natural ventilated urban environment.