Recently, increasing number of high-rise buildings are built in Hong Kong, especially in the urban area. Wind environment of existing buildings is affected significantly by the high-rise buildings. Flow distribution of high-rise buildings closely interacts with existing building, which may influence pollutant distributions at the height of activity of human being. In this paper, the finite volume method was used to investigate the effect of a new high rise building on wind environment of existing buildings, and the pulsating flow was simulated by RNG k-ε model. A suitable computational grid was generated by special methods. A comparison experiment was conducted between the isolated buildings with high-rise building and without high-rise building. A ventilation threat area has been found with its wind speed reaching above 12m/s and an updraft area has also been detected in the case of high-rise building, which may lead to a contamination threat to the downstream buildings.