Abstract: Objective: To evaluate the image quality, radiation dose and clinical application value of the "double low"(low tube voltage and low iodine) technology in the CT pulmonary angiography(CTPA). Method: The patients(n=105) with clinicaliy suspected as pulmonary embolism(PAE), were randomly divided into group A, B and C(each n=35), prospectively. Group A: the tube voltage was 120 kVp, and the volume of contrast agent was 40 mL(Iodine consentration: 350 mg I/mL), flow rate 4 mL/s; Group B: the tube voltage was 100 kVp, and the volume of contrast agent was 35 mL(Iodine consentration: 300 mg I/mL), flow rate 3.5 mL/s; Group C: the tube voltage was 80 kVp, and the volume of contrast agent was 30 mL(Iodine consentration: 270 mg I/mL), flow rate 3 mL/s.Group A was using filter back-projection algorithm(FBP) and both group B and C was using the technology of ASIR for reconstruction, and all groups was opening Attenuation-based online tube current modulation(ATCM) technology. Recording each patient's CTA scan time, the volume of contrast agent, CT dose volume index(CTDIvol) and dose length product(DLP), and calculating the effective dose(ED), type specific dose estimation(SSDE) value and the amount of iodine.To measure the CT values of pulmonary artery trunk, left and right pulmonary arteries and subsegmental Pulmonary in the axial image.To compare the radiation dose, the amount of iodine,and the subjective and objective evaluation index of the image quality by Using Kruskal-Wallis H test. Results: The differences of the measured average CT values of the main pulmonary artery, left and right pulmonary arteries and subsegmental pulmonary artery between the three groups were not statistically significant(P > 0.05); The differences of background noise, SNR, CNR and subjective evaluation between the 3 groups' images were also not statistically significant(P > 0.05). Compared with group A, the ED of group B and C were decreased by 38.09% and 51.99% respectively, and SSDE were decreased by 37.96% and 48.39% respectively. The amount of iodine in the A group was higher than that 25% in the B group and 42.14% in the C group, Conclusion: The application of the tube voltage(80 kVp), the volume of contrast agent(30 mL) and the iodine concentration(300 mg I/mL) and flow rate 3mL/s in CT pulmonary angiography is feasible, not only can the image quality meet the Clinical Diagnosis, but also reduce the radiation dose and the amount of iodine.