In this paper, a new method called TSM (Two Step Method ) was presented to analyze external air movement around buildings .In TSM, the computational process is divided into two steps .In the first order , the computational domain may be much larger than the area we concern and big grids will be used . Besides, the concept of gradient wind was introduced to make inflow boundary conditions closer to actual case. In the second order, the computational domain was diminished to the area we concern, Grids will be redefined in detail. Boundary conditions come from the rough results of the first order. This process can be repeated so as to get satisfactory results .TSM provides an opportunity to solve the problem above in a sense. As an example ,the air movement around a villa cluster was given in the paper as well