Abstract： Objective To summarize and analyse the morphology and distribution of embolus in patients suspected acute pulmonary embolism.Methods The CT pulmonary angiography(CTPA) imagings of 279 patients suspected acute pulmonary embolism were analysed retrospectively in Ningxia from January 2004 through June 2006 and in Beijing from September 2005 through October 2006.The incidence of central embolus,peripheral embolus and mixed embolus,and the distribution and the morphology of embolus in different levels of pulmonary arteries were analysised.Results A total of 279 patients (158 males,121 females; Median age was 63 years) were recruited.The incidence of central embolus,peripheral embolus and mixed embolus were 3.5％,40.9％ and 55.6％,respectively.There were 1850 emboli found above the segmental pulmonary arterial,58.2％ were found in right pulmonary artery,and 41.8％ in left pulmonary artery.For all of the emboli,there were 29.7％ in bilateral upper lobes,18.3％ in midial lobe and lingual lobe,and 49.8％ in bilateral lower lobes.The percent of A,B and C type embolus were 81.7％,7.6％ and 10.7％,respectively.Conclusion It was not unusual for the peripheral thrombosis,and can be improved to detect peripheral thrombosis by thin-slice CT scan.The distribution of embolus in pulmonary vascular and the distribution of blood flow was consistent,the number of embolus in right lung were more than left lung,and lower lobes more than upper lobes and middle lobes.