Abstract: Objective: To observe the features of pathological structure of pneum-arteriolar in complex congenital heart disease with diminutive pulmonary blood. Methods: Twenty-eight patients suffering from congenital heart disease with diminutive pulmonary blood (study group) and 28 matched volunteers (sex,age and body weight) without cardiopulmonary disease (control group) were select to obtain right middle lobe lung tissue pieces (1 cm×1 cm×1 cm) after thoracotomy. Optical microscope was connected biomedical image analysis,the pulmonary arterioles with the diameter ≤ 100 μm and cross-section complete were select to measure the pulmonary arterioles outside and inside diameter of five pulmonary arterioles in lung tissue, and the average percentage of media thickness (mMTPA) was calculate. After taking the average the total vascular area of pulmonary arterioles,vascular lumen area,vessel wall area, vessel wall area/vessel total area (WA/TA),vascular lumen area/vessel total area (EA/TA),and perunit area the number of pulmonary arterioles (APSC) were calculate. Results: The outside diameter of pulmonary arterioles in study group was no significant difference compared with the control group (P > 0.05),and the inside diameter of pulmonary arterioles in study group was higher (P < 0.01),the mMTPA,WA/TA and APSC of pulmonary arterioles in study group was significantly lower (P < 0.01). Conclusions: Tunica media of pulmonary artery was thiner and vascular lumen expanded, APSC of per unit area was reducing in congenital heart disease with diminutive pulmonary blood.