【Abstract】 Objective To study the value of 64  slice 128  slice spiral CT pulmonary angiography in the diagnosis of pulmonary embolism under different conditions. Methods 123 pulmonary embolism patients, according to the injection of contrast agent dose and tube voltage, were randomly divided into conventional dose group (60 cases) and lowdose group (63 cases). All patients were diagnosed by 64slice 128slice spiral CT pulmonary angiography for the second time. The conventional dose group took the tube voltage 120kv and the contrast agent 150ml. The low dose group took the tube voltage 100kv and the contrast agent 35ml. Diagnostic effect was observed. Results The CT values of the left and right pulmonary veins in the low dose group were significantly lower than those in the conventional dose group (P＜005). The overall image quality of the low dose group (8095%) was significantly higher than that of the conventional dose group (4333%) (P＜005). Conclusion 64  slice spiral CT pulmonary angiography with low voltage and low contrast medium can significantly improve the image quality, which is beneficial to the imaging differentiation of the pulmonary arteries and veins, and is feasible in the diagnosis of pulmonary embolism by CT pulmonary angiography.