Abstract： Lungs are located in the chest and lie on both sides of mediastinum.The major function of lung is to balance the external and internal 'gas' environment and to maintain homeostatic equilibrium.Because lung is closely interacted with outside surroundings as well as general circulation,it is fair to say that lung is a delicate organ which may be attacked by so many noxious stimuli,such as bacterial or viral infections,chemical insults (smoke,dust,etc),radiation,autoimmune and allergic responses.Damage to lung tissue can result from these various acute or chronic stimuli,which in tum disrupt lung homeostasis and a dysregulated healing response will eventually occur, such as inflammation,anti-fibrinolytic coagulation cascade and accumulation of pro-angiogenic,and fibrogenic cytokines,growth factors and enzymes.Uncontrolled healing response could gradually evolve into a pathogenic fibrotic response when important checkpoints are missed and inflammation becomes unrelenting.