Abstract： This paper introduces the experience of CHEN Xiangjun treating rheumatoid arthritis complicated with interstitial pneumonia based on syndrome differentiation. The pathogenesis of rheumatoid arthritis complicated with interstitial pneumonia is analyzed. It is believed that deficiency， phlegm and blood stasis are the key factors in the pathogenesis of rheumatoid arthritis complicated with interstitial pneumonia，and the three factors are interrelated and interact as both cause and effect. Syndromes can be differentiated into the deficiency and the excess. The deficiency syndromes mainly include lung- spleen qi deficiency， which should be given the treatment of supplementing the lung and fortifying the spleen； deficiency of both qi and yin，boosting qi and nourishing yin；and lung-kidney deficiency，replenishing lung and kidney. The excess syndromes are phlegm- damp obstructing the lung， which is advisable to dispel dampness and dissolve phlegm； phlegm-heat accumulated in the lung，to clear heat and dissolve phlegm；binding of phlegm and stasis，to dissolve phlegm and stasis and unblock the collaterals. On medication，deficiency，phlegm and blood stasis are always treated together，and heat-clearing and toxin-resolving drug and carbuncle-resolving and boil-expulsing drugs are well used.