In this paper, we studied the pulmonary artery mechanical properties of the patient with chronic pulmonary hypertension. We selected the patients with pulmonary hypertension secondary to rheumatic mitral valvular disease, and measured pulmonary thenal resistance and compliance. The results showed a significantly lower in the pulmonary artenal compliance (Co) and resistance of patients with pulmonary hypertension as compared to the controls (p<0.01). Linear correlation analysis showed that preoperative PAPm correlated closely with Co (r=0.745, p<0.05). we measured the changes of the pulmonary circulation hemodynamics and arterial compliance while infusing Sodium Nitroprusside(0. 5 ug/min' kg). In group of mild pulmonary hypertension (PAPm