Objective To research optimizing the technology of multislice spiral CT pulmonary angiography. Methods The 56 patients with clinically suspected pulmonary embolism were randomly divided into A, B groups. Every group has 28 patients. Contrasting agent trigger automatic tracking technology and Tube current automatically triggered were used for multislice spiral CT pulmonary angiography (CTA) examination. Group A was test group with 80 kVp tube voltage. The superior vena cava was selected for ROI monitoring plane with the preset threshold of 80HU. The contrast agent used non-ionic contrast medium iohexol 300mgI/ml.The dose was 60ml.The injection rate was 4ml/s.The vein was immediately flushed with 40 ml brine after the contrast agent losers. Group B was contrast group with 120 kVp tube voltage. The pulmonary root opening was selected for ROI monitoring plane with the preset threshold of 100HU. The contrast agent used non-ionic contrast medium iohexol 370 mgI/ml.The dose was 60ml. The vein was immediately flushed with 20 ml brine after the contrast agent losers.The image quality was evaluated after lung CTPA scanning. Results There is no statistically significant difference between two sets of image quality. The radiation dose of Group A was decreased 38% than group B. The entered iodine dose of Group A patients was decreased 19% compared with group B. The image was clarity with superior vena cava as the ROI detection plane and 80HU as the threshold . In this case the ascending aorta without contrast agent filling,The pulmonary angiography was agent filled favorably. The artifacts of the superior vena cava of 40ml saline was significantly reduced than 20ml. Conclusion By optimizing conditions of pulmonary imaging scanning,it can significantly reduce the radiation dose and the intake of the total iodine. The image quality can meet the needs of clinical diagnosis.