Abstract: Objective: To investigate the value of energy spectral CT in the diagnosis of acute pulmonary embolism and pulmonary perfusion changes. Methods: A retrospective analysis of 43 cases of suspected acute pulmonary embolism from November 2017 to July 2019, all patients with suspected acute pulmonary embolism underwent enhanced spectrum scanning, and the original data images reconstructed pulmonary angiography images and iodine-based substances at the workstation. Observe and record the location and number of pulmonary emboli; analyze the location and number of intrapulmonary perfusion reduction zone in the iodine-based substance map, and measure the iodine value and CT value of the intra-poor hypoperfusion zone, and measure the normal lung of the same level or adjacent level Substantial iodine value and CT value. The chi-square test was used to compare the number of emboli detected by the mixed energy image with the best single-energy image. The two-sample rank sum test was used to compare the iodine value and CT value between the perfusion reduction zone and the normal zone. RESULTS: A total of 12 patients with pulmonary embolism were diagnosed. A total of 256 emboli were found by mixed energy imaging. Among them, 22 were central emboli (pulmonary trunk and lobes), and peripheral type (pulmonary and lung sub-emboli) 234. There were 58 fully occluded emboli and 198 non-completely occluded emboli. A total of 273 emboli were found by the best single-energy image observation, including 22 central emboli (pulmonary trunk and lobes) and 251 peripheral (pulmonary and pulmonary emboli); fully occluded embolus 74, 199 non-completely occluded emboli. The best single-energy image had a higher detection rate than the mixed energy image in the diagnosis of peripheral and fully occluded emboli, but the difference was not statistically significant (P>0.05). The intrapulmonary perfusion reduction area was 42, the perfusion reduction area ((2.70±1.81) 100ug/mm³, (-829±45.94) HU) and the normal area lung field ((17.78±3.29) 100ug/mm³, (-741±34.34) HU) iodine value, CT value for comparison, the difference was statistically significant (P<0.05). Conclusion: Energy spectral CT can be used for qualitative and local diagnosis of pulmonary embolism. Iodine-based substance map can evaluate pulmonary blood perfusion changes and provide information for evaluating pulmonary embolism.