This study aimed to evaluate the values of thoracic multi-slice spiral computed tomography (CT) in the diagnosis of incidental pulmonary thromboembolism (IPTE) in patients with malignant tumors. The clinical data and imaging features of a total of 1,684 patients with malignant tumors, treated in the Fourth Hospital of Hebei Medical University, were analyzed retrospectively in order to investigate the types of malignancies, the patients' clinical features, and the emboli-preferred sites. Among the 1,684 patients, 60 patients had experienced IPTE (3.56%), 35 were females (58.33%), 25 were males (41.67%). Lung cancer had the highest incidence (n=22, 36.67%). The most common site of IPTE was the left lower lobe of pulmonary artery (n=46, 76.67%). The imaging results revealed that in 5 patients (8.33%) IPTE did not occur. Thoracic multi-slice spiral CT has a high detection rate of IPTE in patients with malignant tumors. Early diagnosis is helpful for early clinical treatment and has significant importance for patients' prognosis.