Abstract: Objective: To investigate the feasibility of 39 mL low contrast agent injection adopted for 320-row CT coronary artery imaging. Methods: Sampling among 100 patients (52 males and 48 females) with 320-slice CT coronary angiography for consistent data collection. The patients were randomly divided into low contrast group and control group with 50 patients respectively. The low-contrast agent group adopts three-phase injection protocol with 39 mL contrast agent in total, while the control group receives 50 m L contrast agent injection protocol for two phases. Measure and compare CT values of main blood vessels, signal-to-noise ratios and contrast-to-noise ratios. Then the coronary arteries are evaluated and analyzed by two experienced doctors. Results: There is no statistical difference reflected from gender ratio, age, weight, BMI, average heart rate during exposure, aortic root noise, SNR, superior vena cava, CNR^RCA1, and CNR^LM between the two groups (P>0.05). Meanwhile, the comparison of CT values of arterial root, right atrium, right ventricle, RCA1, LM, and ventricular wall of the two groups reveals a statistical difference (P<0.05). Among 1217 coronary segments, 94.91% (1155/1217) segments meet the diagnostic image quality requirement. The image quality acceptability rates of the low contrast group and the control group were 95.4% (555/582) and 94.5% (600/635) respectively, which reflects few statistical difference (P>0.05). Conclusion: It's feasible to use a small-dose (39 mL) contrast agent injection in 320-slice CT coronary angiography with three-phase injection protocol, which is able to form qualified diagnosis images with less contrast agent injection.