〔Abstract〕 ObjectiveTo investigate the diagnostic value of ultra-high resolution CT in pulmonary focal ground glass nodule (fGGN) less than 3 cm. Methods A total of 96 patients with fGGN smaller than 3 cm admitted to Longyan First Hospital from January 2020 to June 2022 were selected as the research objects. All patients underwent high-resolution and ultra-high-resolution CT examination. Results Among the 96 patients with fGGN, 3 had atypical adenomatous hyperplasia (3.13 %), 49 had invasive adenoma (51.04 %), 25 had carcinoma in situ (26.04 %), and 19 had microinvasive adenoma (19.79 %). Compared with high resolution CT, high resolution CT showed a higher lobular detection rate and a higher proportion of clear polish at the tumorlung interface, the differences were statistically significant (P < 0.05). Compared with high resolution CT, the diagnosis rate of high resolution CT was higher, and the difference was statistically significant (χ 2 = 27.148, P < 0.001). The contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR) and image noise score of ultra-high-resolution CT were lower than those of high-resolution CT, and the differences were statistically significant (P < 0.05). Conclusion In the diagnosis of fGGN smaller than 3 cm, the ultrahigh resolution CT examination can more effectively diagnose the segmentation sign and the tumor lung interface, and the definite diagnosis rate is significantly higher than that of high resolution CT examination. The ultra-high resolution CT examination has more obvious background noise, and the high CNR and SNR scores are relatively lower. Although artifacts caused by center jump and breathing during examination may affect the results of ultra-high resolution CT examination to a certain extent, they have no significant impact on its clinical diagnostic efficacy.