Objective To investigate the changes of pulmonary diffusing capacity and pulmonary capillary blood volume in stable COPD patients with mixed ventilation dysfunction, and explore the possible pathophysiological factors. Methods 159 stable COPD patients with mixed ventilation dysfunction were recruited in the study and 36 normal subjects were recruited as control. The Belgium medisoft box5500 was used to determine the pulmonary ventilation function, lung capacity, and pulmonary diffusing capacity. The measured parameters included forced vital capacity ( FVC) , forced expiratory volume in one second ( FEV1 ) ,maximal voluntary ventilation ( MVV) , vital capacity ( VC) , total lung capacity( TLC) , residual volume ( RV) , minute volume of alveolar ventilation ( VA ) , lung diffusing capacity for carbon monoxide ( DLCO) , pulmonary membrane diffusing capacity for carbon monoxide ( DMCO) , and pulmonary capillary blood volume ( Vc) . The above parameters were compared between the COPD patients and the normal subjects. The relationship was analyzed between DLCO% pred, DMCO% pred, Vc% pred and all the ventilation parameters. Results In stable COPD patients with mixed ventilation dysfunction, all parameters of pulmonary ventilation function, lung capacity, and pulmonary diffusing capacity were significantly different from the normal subjects ( Plt;0. 05 or Plt;0.01) . FVC, VC, VA, and DMCO of the COPD patients were about 66% of the calculated value or more. The average TLC%pred was a little higher than the normal. FEV1 , MVV, DLCO and Vc were abnormally lower which were between 36% ～44% . The average RV%pred was 188% of the predicted value. Obvious correlation could be detected between DLCO% pred, DMCO% pred, Vc%pred and FEV1%pred, FEV1/FVC, TLC% pred, RV%pred, RV/TLC and VA% pred etc.Conclusions In COPD patients with mixed ventilation dysfunction, the pulmonary blood capillary is damaged seriously which lead to a significant decrease of the capacity of pulmonary blood capillary, as well as seriously air distribution disturbance and ventilation/bloodstream mismatch. The Vc decline may develope before the impairment of pulmonary diffusing capacity which may contribute to the damaged of DLCO and DMCO.