Objective To investigate the imaging features of energy spectrum CT in patients with pulmonary embolism (PE) and its relationship with right heart function and prognosis. Methods 90 PE patients admitted to our hospital from May 2022 to May 2024 were retrospectively collected and included in the observation group. At the same time, 50 healthy subjects who underwent physical examination in our hospital during the same period were selected as the control group. PE patients were divided into mild PE group (50 cases) and severe PE group (40 cases) according to the severity of the disease. According to the different prognosis of PE patients, the observation group was divided into a good prognosis group (58 cases) and a poor prognosis group (32 cases). The embolization score, defect score and right and left ventricular short axis maximum diameter ratio (RV/LV) were calculated by energy spectrum CT in all subjects. The value of embolization score and defect score in prognosis was analyzed by ROC curve. Results The results of energy spectrum CT showed that there was no defect in the control group, while the PE patients showed varying degrees of pulmonary field brightness increase, pulmonary texture change and pulmonary artery blockage. The mild PE group mostly showed spotty and patchy defects, while the severe PE group mostly showed subsegmental or segmental defects. The defect score and embolization score in severe PE group were significantly lower than those in mild PE group, while RV/LV was significantly higher in mild PE group (P<0.05). The defect score and embolization score in the poor prognosis group were significantly lower than those in the good prognosis group (P<0.05), and RV/LV in the poor prognosis group and the good prognosis group had no significant difference (P>0.05). ROC curve results showed that defect score was more valuable than embolization score in predicting the prognosis of PE, and the area under the curve reached 0.911. Conclusion Energy spectrum CT can accurately reflect the degree of lesion and right heart function in patients with pulmonary embolism, and defect fraction has a high value in prognosis.