Objective：To investigate the feasibility of a contrast agent injection protocol based on body mass index（BMI） multiplied by injection coefficient in 256-slice spiral computer tomography（CT） for coronary computed tomographic angiography（CTA）. Methods：A total of 300 patients with the symptom of chest pain who underwent coronary CTA were randomly divided into groups A，B，and C. The injection rate was 0.15×BMI（mL/s） in group A，0.20×BMI（mL/s） in group B，and 0.25×BMI（mL/s） in group C，and the amount of contrast agent was calculated based on injection rate×9. Image quality was evaluated after scanning，and the concentration of the contrast agent was measured at the root of the aortic valve and at the opening of the left anterior descending coronary artery（LAD），the proximal portion of the left circumflex artery （LCX），and the right coronary artery（RCA）. Results：Group B had a signifi－cantly higher excellent rate of image quality than the other two groups. There were significant differences between the three groups in the CT values of the aorta and the three important branches of the coronary artery（LAD，LCX，and RCA）（P<0.001）. There was no significant difference in noise between the three groups（P>0.05），while signal-to-noise ratio and contrast/noise ratio gradually in－creased from group A to group C. Conclusion：Injection rate and amount of contrast agent based on BMI multiplied by injection coef－ficient for coronary CTA can meet the needs of clinical diagnosis and significantly reduce the amount of contrast agent.