Objective To investigate the application value of dual source 128 slice spiral CT in the diagnosis of pulmonary artery hypertension which caused by interstitial lung disease of connective tissue disease. Methods A total of 60 cases of connective tissue disease with pulmonary artery hypertension from January 2013 to May 2015 in our hospital were rolled into the study. 60 PAH patients and 42 cases of normal cases accepted pulmonary CT angiography examination, and the results were analyzed. Results 55 cases showed the expansion of the main pulmonary artery in the PAH group, the accuracy of CT diagnosis is 86.67% (52/60), MPAD, rPA, rPD values were higher than the control group (P<0.05). The diameter of main pulmonary artery (MPAD), right pulmonary artery(RPAD), left pulmonary artery(LPAD), right inferior pulmonary artery (RLLPAD) of PAH group was significantly higher than the control group (P<0.05). The specificity, sensitivity, negative value and positive predictive value of the main pulmonary artery diameter over 2.9 cm predicted that were 85.5%, 87.6%, 87.4%, 85.4%. Conclusion Multi slice spiral CT has high spatial resolution, and gets the high quality CT images of the pulmonary artery which helps the diagnosis of PAH, and deverse spreading.