| Asthma is a kind of series chronic disease in chest, it is a main reason which causes man die, the rate of people get this disease are much more than before as long as the human's society become more industrialism. There is a problem that no one can fully explain the reason of what the asthma is going on. It is said that this disease is a result of stimulating by force actor combine with chemical reason when the lung get inflammation. So it is useful to know how the lung work in normal time and the responsibility when we gave some stimulate to it.The lung is a very important organ which in charge process of the body exchange oxygen and CO2 from air. It moves every minute, so it must take some force factor to influent itself. If we know more well the lung's properties in both health and ill state, the more airway illness we can prevent. But the structure of the airway is too complicate to monitor by our own eyes, so the tool of computational fluid dynamics show its'powerful effect that we can supervise the process of how the lung get illness.Computational Fluid Dynamics (CFD) is a kind of finite element methods (FEM). It solves the equation of Na?ve-Stokes (N-S) by a numerical way for solving that equation on the other way is too difficult. This method has been a popular way to manufacture new tools just like airplane.In this paper we use computed tomography (CT) scaned a real healthy man's chest,and then loaded this file into geometric-file-conversion software to generate a 3D airway geometry model.We analyzed the 3D model in ANSYS-CFX for fluid properties,sumulated the process that set the borader conditon as some small airways shutdonwn one by one just like the athsma occurred,analsys the condition of presure and velocity in and on the airway.We found that when that situation happened,the neighbor small airways would be shutdowned together with those has been closed ,so avalanche occucred and then transformed into the diesease–Athsma.
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