Objective: To explore the value of percentage of CT value increment, CT value and CT value increment for differentiating the pathologic character of pulmonary ground-glass nodules. Methods: Altogether 59 cases and 63 pure ground glass nodules pathologically diagnosed as preinvasive lesion at Ruijin Hospital and Renji Hospital affilia-ted to Shanghai Jiao Tong University School of Medicine from December 2012 to December 2018 were collected. The pathological classification were atypical adenomatous hyperplasia (AAH) (18 cases) and adenocarcinoma in situ(AIS）(45 cases). Their imaging manifestations were pure ground glass nodules. The diameter of AAH and AIS was ≤1.5 cm. The percentage of CT value increment, CT value and CT value increment of pure ground glass nodules and lung CT value were measured. The percentage of CT value increment denotes the percentage of increment of nodules CT value over lung CT value; CT value increment denotes the increment of nodule CT value over lung CT value. Student's t-test, binary regression analysis and receiver operation characteristic curve were used to analyze the value for differentiating AAH and AIS. Results: When cutoff values were taken as percentage of CT value increment of pure ground glass nodule 25%, CT value -615 HU and CT value increment 223 HU, they were helpful for differentiating AAH from AIS（P<0.05）. The sensitivity for diagnosis of AAH were 78%, 76% and 100%, respectively; the specificity were 62%, 77% and 71%, respectively. The area under the ROC curve were 0.83, 0.86 and 0.80, respectively. Conclusions: The percentage of CT value increment, CT value and CT value increment of pure ground- glass nodules are helpful for differentiating AAH and AIS.