Objective To explore the feasibility of coronary artery computed tomography (CT) angiography in patients with body mass index (BMI)≤30 kg/m² using 320-slice CT with 70 kV tube voltage and low contrast agent dose and flow rate.Methods Fifty-two consecutive patients with BMI≤30 kg/m² and suspected or diagnosed coronary artery diseases were enrolled in our hospital from Jan.to Apr.2021.The data were collected by wide detector CT prospective electrocardiographically-gated axial scan mode.All the patients were randomly divided into 2 groups:70 kV group (using 70 kV tube voltage and low contrast agent dose and flow rate) and 120 kV group (using 120 kV tube voltage and conventional contrast agent dose and flow rate).In both groups,images were reconstructed using a hybrid iterative algorithm.Patients’ age,weight,BMI,heart rate,amount of contrast agent and flow rate were statistically analyzed to evaluate the objective and subjective image quality of the vessels in each segment of the coronary arteries,and radiation doses of the 2 groups were analyzed and compared.Results The contrast agent dose and flow rate in the 70 kV group were significantly lower than those in the 120 kV group (［ 27.15±3.70］ mL vs［ 48.92±5.08］ mL,［ 2.71±0.37］ mL/s vs［ 4.50±0.35］ mL/s,both P＜0.001).There were no significant differences in coronary mean CT values,signal to noise ratio or contrast to noise ratio between the 2 groups of patients in objective image quality measures (all P＞0.05),while the image noise of the 70 kV group was significantly higher than that of the 120 kV group (［31.50±5.74］ HU vs［28.26±5.17］ HU,P＝0.037).A total of 770 coronary artery segments were included for the subjective assessment,and the image subjective rating agreement between the 2 observers was good (Kappa＝0.772).There were no significant differences in coronary artery subjective quality average score or excellent and good rate between 70 and 120 kV groups (1.71±0.38 vs 1.21±0.43,100.00%［ 384/384］ vs 98.96%［382/386］,both P＞0.05).The effective dose,CT volume dose index and dose-length product were significantly lower in the 70 kV group than those in the 120 kV group (［0.80±0.16］ mSv vs［3.13±0.67］ mSv,［4.51±0.98］ mGy vs［17.36±3.19］ mGy,［57.32±11.32］ mGy·cm vs［223.61±47.64］ mGy·cm,all P＜0.001).Conclusion It is feasible to use 320-slice CT with 70 kV tube voltage for coronary angiography in patients with normal BMI.Under the condition of sub-mSv,images meeting the clinical diagnosis can be obtained,and the dose and flow rate of iodine contrast agent are greatly reduced compared with the conventional scan mode.