Objective To investigate the correlation between CT features of MIA and IAC and fibrosis within tumors. Methods The preoperative CT images of 43 ground glass nodules in 42 lung adenocarcinomas were retrospectively analyzed. The fibrosis within tumors was graded semi-quantitatively. Pleural indentation and lobulation, spiculation, abnormal blood vessels, abnormal bronchi and interstitial fibrosis grade of tumor quantitatively between MIA and IAC were analyzed by rank-sum test and chi-square test. Spearman test was made to analyze correlation between CT features and interstitial fibrosis grade of tumor. Results (1) The extent of lobulation and pleural indentation ,the amount of spiculation, abnormal blood vessels and bronchi were statistically significant difference between MIA and IAC(P<0.05). (2)There were also significant difference in the terms of the degree of fibrosis within tumors between MIA and IAC(P<0.05). (3) The grade of fibrosis in tumor is significantly positively related to the extent of pleural indentation(r=0.496, P<0.05) and lobulation(r=0.440, P<0.05), the amount of spiculation(r=0.305, P<0.05) and abnormal blood vessels(r=0.372, P<0.05), there is no obvious correlation between the grade of fibrosis in tumor and the amount of abnormal bronchi(r=0.173, P>0.05). Conclusion The extent of pleural indentation and lobulation, the amount of spiculation and abnormal blood vessels on CT can reflect the grade of fibrosis in lung adenocarcinoma, which have important value of clinical application in the preoperative differential diagnosis of MIA and IAC.