Objective To evaluate image quality and radiation dose under low concentration of contrast agent and low tube voltage for head and neck CTA by using of 320-row CT with a "double low" scanning protocol. Methods 60 patients, who underwent head and neck CTA with a 320-row CT scanner, were divided into two groups randomly. 30 patients (group A) received 120 kV voltage and ultravist (370mgI/ml), and the remaining 30 patients (group B) received 100 kV voltage and iodixanol (270mgI/ml). CT values, standard deviation of intracranial arteries and image noise on the corona radiate were measured to calculate contrast-noise-ratio(CNR).Then recorded dose length product and calculated the effective radiation dose. The above all data used two independent sample t test for statistical analysis. Results Image quality of two groups were conform to the requirements of diagnosis. The CT value and CNR of head and neck artery had no significant difference between two groups(P＞0.05).The dose length product and the effective radiation dose of group A were higher than group B, and there were statistically significant difference between them(P＜0.05). Conclusion Image quality of head and neck CTA by the scanning protocol (100kV+iodixanol) of 320-row CT scanner can meet the requirement of clinical diagnosis, and effectively reduce the radiation dose.