From the perspective of “lung is blood viscus”，this paper combined modern clinical and scientific research to understand and analyze the effect of collateral vessels on idiopathic pulmonary fibrosis.It is known that the collateral vessel is the channel for qi and blood circulation in the body，which plays a key role in the qi and blood circulation.The theory of “lung is blood viscus” believes the disorder of qi and blood may eventually lead to lung stasis，phlegm obstruction and blood stasis，and lung collateral block，forming pathological products of phlegm，stasis，toxicity，and deficiency.The lung without nourishment for a long time finally develops interstitial lung disease，and becomes weak and dysfunctional.The author believed that based on the theory of “lung is blood viscus”，the lung was easy to be blocked，and the blood was easy to enter but difficult to exit.The lung deficiency was the basis of the formation of interstitial lung disease.The block of collateral vessels and qi stagnation and blood stasis were the pathogenesis of idiopathic pulmonary fibrosis.The theory of collateral disease，in turn，proved the theory of “lung is blood viscus”.Clinically，the method of tonifying lung，replenishing qi，activating blood，and dredging collaterals should be applied throughout the treatment process of the disease.