Abstract: OBJECTIVE To investigate core medicine and their relationship in formulas for lung distension to explore the compatibility law. METHODS After researching all prescription literatures， 194 formulas for lung distension were selected and analyzed by correlation analysis and hierarchical clustering analysis. RESULTS The results of correlation analysis showed medicine whose support was more than 20% were glycyrrhiza， almond， ephedra， pinellia， poria， tangerine peel and schisandra chinensis， and as well as some medicine groups， including almond-ephedra-glycyrrhiza，ephedra-glycyrrhiza-pinellia and ephedra-schisandra chinensis-asarum. The results of hierarchical clustering analysis showed medicine warming the lung to resolving phlegm including ephedra， glycyrrhiza， pinellia， rhizoma zingiberis， cassia twig，schisandra chinensis and asarum. Medicines clearing the lung to remove heat include gypsum fibrosum， almond， ephedra and glycyrrhiza， medicine regulating qi and dissipating phlegm include tangerine peel， citrus aurtantium， and balloonflower. Medicines activating blood to resolve blood stasis and phlegm include angelica， peach kerne， ligusticum chuanxiong， succus bambusae and medicines fortifying the spleen and warming the kidney include aconite， atractylodes and poria. CONCLUSION The lung distension prescriptions may ventilate the lung to remove palegm， warm the lung to reduce fluid， clear the lung to remove heat， activate blood to resolve blood， as well as warm the kidney and fortify the spleen. This study is useful for clinical application in treating lung distension-related diseases based on syndrome differentiation.