Objective To investigate diagnostic value of CT plain scan and Tri-phase Enhancement scan in pulmonary nodules. Methods Used to analyze 56 patients our hospital from 2016 May-2017 June were selected to study by A retrospective analysis. Patients were treated with CT plain and three enhanced scan for two weeks after admission, and were diagnosed as pulmonary nodular lesions by surgical and pathological examination. Results There were 26 cases of benign nodules patients and malignant nodules patients in 51 cases. Comparing the average CT value by CT plain, there was no difference between benign nodules and malignant nodules (P>0.05), and compared with benign nodules, the average CT value of malignant pulmonary nodules by CT enhanced scan 60s benign was alleviated significantly (P<0.05). There was no statistically significant difference between the CT values of enhanced scan 15s and 30s (P>0.05). The CT added value between 20-60 HU was treated as malignant nodules. The sensitivity of the CT three phase enhanced scan to the diagnosis of malignant nodules was 92.86%, the specificity was 86.73%, and the diagnostic accuracy was 81.46% by measuring maximum net value of CT between 20-60HU of malignant nodule. Conclusion CT plain scan and three phase enhanced scan have high diagnostic accuracy in pulmonary nodules, and have certain differential diagnosis value for benign and malignant.