Abstract: Objective: To study the effect of different triggering thresholds on the quality of pulmonary artery CT angiography (CTA) images. Materials and Methods: A prospective study included 112 patients with suspected pulmonary embolism admitted to Tinglin Hospital in the Jinshan District of Shanghai between December 2021 to April 2023. Among them, there were 49 males and 63 females aged between 37 and 93 years, with an average age of 64.28 years. Patients were randomly assigned to three groups based on trigger thresholds. Group A included 38 cases with a trigger threshold of 120 HU, Group B included 37 cases with a trigger threshold of 200 HU, and Group C included 37 cases with a trigger threshold of 250 HU. There were no statistically significant differences in gender, age, height, or weight among the three groups. One-way ANOVA was used to compare the CT values and subjective image quality scores of the superior vena cava, main pulmonary artery, left and right pulmonary arteries, and right pulmonary vein among the three groups. Result: There were no statistical differences in the CT values of the main pulmonary artery and left and right pulmonary arteries among the three groups, but there were statistical differences in the CT values of the superior vena cava and right pulmonary vein. There was a statistical difference in the subjective score of image quality among the three groups; the subjective evaluation of the obtained image quality between the two physicians was highly consistent (κ=0.78). Conclusion: When the triggering threshold of pulmonary artery CTA is 200 HU, it can not only ensure the concentration of pulmonary artery trunk CT value meets the clinical diagnosis, but also ensures that the contrast agent is fully injected into the 5~6 grade branches, leading to less retention of superior vena cava, weak pulmonary vein development, and the highest image quality of pulmonary artery CTA.