Objective To explore the methodological difference in lung nodule size and density measurement and its value in accurate diagnosis of lung adenocarcinoma in situ. Methods 97 patients 63 females, 34 males, age ranged from 24 to 79yrs, mean (50.3±12.0) yrs, with lung adenocarcinoma in situ lesions confirmed by operation pathology were included in this study. All the cases were performed ultra-high-resolution computed tomography before operation. Results 100 cases of lung AIS, including 81 pure groundglass nodules and 19 mixed ground-glass nodules. The maximum and average diameter of pGGNs were smaller than mGGN in lung AIS. In mGGN, the maximal diameter of solid component was (4.2±1.4)mm, the average diameter of solid component was (3.7±1.2)mm. The average CT value of homogeneous pGGNs were (-637.2±101.5) HU, inhomogeneous pGGNs were (-566.7±99.8)HU, the average CT value of the representative region in it is (-438.6±117.2)HU. The average CT value of the 81 pGGN was (-599.7±106.1)HU. Conclusion The lesions of lung AIS were judged mainly by the size and density of the lesion. The pGGNs were smaller than mGGNs in lung AIS. The average CT value in homogeneous AIS lesions were lower than inhomogeneous lesions, the higher density section provides the basis for distinguishing aggressive components.