Abstract: Object: To study the value of CT in diagnosis of sinonasal inverted papilloma (SNIP). Methods: 48 cases of SNIP proved by operation and pathology were reviewed retrospectively. Results: Among 48 cases of SNIP, male patients accounted for the majority (62.5%). Rhinobyon and rhinorrhoea were main clinical symptoms (100%), 50% of the patients were accompanied with blood in rhinorrhoea, 31.25% presented hyposmia, 18.75% presented anosmia, 12.5% had a relapse with postoperative 6 years. Among 48 cases, there were 45 cases of unilateral lesions (93.75%). Lesions were most frequently involved ipsilateral maxillary sinus (55.56%). CT plain scan of all SNIP cases showed nasal sinuses soft tissue density mass, and CT value was (45.61~1.02) HU. There were 21 cases of lumps completely filling with involved sinus cavity (43.75%), and 22 cases of lumps incompletely filling with involved sinus cavity (45.83%). In addition, 21 cases of involved sinus cavities presented mild expansion changes (43.75%), 42 cases presented bone absorption or damage of sinus wall and turbinate (87.5%), 7 cases presented affected sinus cavity smaller than the normal-side sinus cavity (14.58%), and 2 cases were limited to nasal polyploidy changes (4.17%). Conclusions: SNIP has a certain CT characteristics, and preoperative CT examination can accurately determine SNIP-involved position and range and can provide an important reference basis for surgical treatment.