Abstract: objective: To compare the effects of two kinds of contrast medium injection projections on the contrast media dose in abdominal aorta combining lower extremity arteries CT angiography. Methods: 50 cases of patients who were suspected abdominal aorta-lower extremity arteries diseases and undergone CT angiography were divided into two groups(A and B) randomly, the contrast media dose was 350 mg I/m L. 16 males and 9 females in group A, the mean age was(58.53 ± 9.39), the mean body weight was(67.86 ± 11.65) kg and the mean scanning range was(124.65 ± 8.28) cm; 17 males and 8 females in group B, the mean age was(60.87 ± 9.76), the mean body weight was(66.23 ± 12.42) kg and the mean scanning range was(122.59 ± 9.12) cm. The injection rate in group A was 4m L/s and total dose was 1.5 m L/kg; in group B, the injection rate was 5 m L/s and total dose was 20 m L in the first step, and the others was injected with 3 m L/s in the second step, and the total dose in group B was equal to 1.5 m L/kg multiply weight and substract(4 m L/s multiply the time difference in two groups). The 30 m L normal saline was injected immediately after contrast medium injection in two groups, and injection rate was 3 m L/s. The intelligent touch scanning technique was used in two groups and the monitor plane was abdominal aorta(the level of right diaphragm), the ROI threshold value was ≥ 150 HU. Scored the five artery sections image quality, measured the CT values of five artery sections, recorded the contrast medium dose in two groups. The independent sample <i<t</i< test was used. Results: The image quality scores and CT values of five artery sections in group A was:(4.76 ± 0.44),(328.46 ± 21.45) HU(abdominal aorta section);(4.20 ± 0.58),(330.96 ± 22.52) HU(iliac artery section);(4.36 ± 0.57),(327.16 ± 23.65) HU(femoral artery-popliteal artery section);(3.32 ± 0.63),(296.53 ± 20.43) HU(crus artery section);(3.12 ± 0.53),(257.26 ± 21.21) HU(acrotarsium artery or planta artery); the data in group B was:(4.72 ± 0.46),(329.75±23.12) HU(abdominal aorta section);(4.08 ± 0.57),(331.63 ± 24.64) HU(iliac artery section);(4.16 ± 0.55),(319.89 ± 21.79) HU(femoral artery-popliteal artery section);(3.24 ± 0.66),(290.44 ± 21.57) HU(crus artery section);(3.28 ± 0.46),(243.76 ± 27.29) HU(acrotarsium artery or planta artery), the data in group B were all worse than that in group A, but there were no statistically significant difference; the contrast dose were(93.79 ± 13.68) m L and(74.61 ± 14.76) m L, there was statistically significant difference. Conclusion: It can obviously reduce the contrast medium dose of abdominal aorta combining lower extremity artery CT angiography that we use the 5 m L/s add 3 m L/s injection step in the premise of not affecting the image quality.