Objective：To explore the visibility of thrombus in the pulmonary trunk on plain computed tomography（CT） scan and its influencing factors. Methods：A retrospective analysis was performed on the clinical and radiological data of 79 patients who were diagnosed with thrombus in the pulmonary trunk by CT pulmonary angiography（CTPA） from June 2017 to October 2018. Based on the CTPA results，the visibility and characteristics of thrombus in the pulmonary trunk on plain CT images were evaluated；the rela－tionship of thrombus features on plain CT images with diameters of the pulmonary artery and ventricular cavity and related laboratory indices was evaluated. Results：In the 79 patients，6（7.5%） had simple main trunk embolism，40（50.6%） simple distal trunk embolism，and 33（41.9%） main trunk embolism with distal embolism. According to the plain CT images，34（43.0%），23（29.1%），and 22（27.9%） patients had intravascular thrombus of low，equal，and high densities，respectively. There was a significant difference in the CT value of thrombus between the three groups[（21.5±6.1） HU vs. （37.9±7.7） HU vs. （63.4±7.0） HU，P=0.000]. However，there was no significant difference in the CT value of blood in adjacent vessels between the three groups[（45.4±7.9） HU vs. （38.6±5.0） HU vs. （40.7±5.2） HU，P>0.05]. According to the CTPA images，the most common type of thrombus was central type（30 patients，38.0%），followed by acute angle with the vessel wall（25 patients，31.6%），and obtuse angle with the vessel wall（16 patients，20.2%）. Conclusion：For patients with suspected pulmonary embolism，a high possibility of thromboembolism should be considered when high- or low-density patchy shadows are detected in the center or one side of the pulmonary trunk lumen on plain CT scan.