In this paper a new method called TSM was presented to analyze wind effect on high-density building areas. With TSM, a software named WEATHER is developed based on STACH-3. The wind effect on a simple building is simulated to validate STACH-3 for outdoor airflow. The wind effect to a real zone with 9 buildings is analyzed with WEATHER. It shows that TSM is an effective method to deal with high-density building areas. It takes an acceptable CPU time to get convergence.