Objective To study the relevant factors and prevention of X-ray missed diagnosis in rib fracture.Methods 28 cases of rib fracture in the X-ray missed diagnosis were retrospectively reviewed. The relevant factors and preventive question of X-ray missed diagnosis were explored.Results Careless reading of film(n=3),wrong position of taking film(n=7),film of low quality(n=4),image of rib fracture concealed by other image (n=11) and improper time of taking film(n=3) were found as the cause of missed diagnosis.Conclusions The X-ray examination of chest is the most practical method in diagnosing rib fracture. The choice of position in taking film,quality assurance of film,the right time in taking film and carefulness in reading film may affect the diagnosis of rib fracture.