Objective To evaluate the diagnostic value of the 4 CT signs of occult fracture of the ribs. Methods The clinical and imaging material of 20 cases with 21 occult rib fractures conformed with CT follow up were evaluated retrospectively. 3 senior radiologists with more than 3 years experiance of image diagnosis reviewed the CT images of the 20 cases and diagnosed the occult fracture blindly in consonance, according to the finding of the 4 CT signs: denser line sign (DL), cortical notch sign (CN), cortical cock up sign (CC) and tiny crack sign (TC). With the rib fractures shown by CT follow up as gold standard, calculated the number of occult fractures of true positive, true negative, false positive and false negative diagnosed with the 4 CT signs, and computed the sensitivity, specialty, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of diagnosis with the 4 CT signs. Results 15 true positive (71.43%), 459 true negative, 5 false positive and 6 false negative diagnosis of rib occult fracture were made with reviewing CT images of the 20 cases on the basis of 4 CT sings blindly, and the sensitivity, specialty, accuracy, PPV and NPV were 71.42%, 98.92%, 98.75%, 75.0% and 98.71% respectively. Conclusion With the signs of DL, CN, CC and TC, occult fractures of the ribs could be detected effectively. Familiar those CT signs might reduce the missed diagnosis of rib occult fracture of the patient with thoracic trauma.