Objective To study the effect of scan triggering threshold technique on the image quality of CT coronary angiography. Methods 75 cases of patients with coronary heart disease (CHD) who underwent dual-source CT coronary angiography in our hospital between February 2015 and January 2016 were selected, including 46 male cases and 29 female cases, BMI < 23. They were randomized into 3 groups: 25 cases in group A, and the triggering threshold value was 120HU. 25 cases in group B, and the scan triggering threshold was 130HU. 25 cases in group C, and the scan triggering threshold was 140HU. According to the patient's body mass index (BMI), patients were scanned after injection of contrast agents. The mean values of CT and SD in the left coronary opening, right coronary opening, left anterior descending branch and left anterior descending branch were measured. According to the measured results, the image signal to noise ratio (SNR) and contrast to noise ratio (CNR) were calculated as the objective basis for image quality assessment. The coronary artery image quality was evaluated by 2 experienced doctors with double blind method. The differences of indexes and image quality under different triggering thresholds were analyzed. Results The SD value of enhanced scan in group B was lower than that of group A and group C2 group, and SNR was also lower than that of group A and group C2 (P<0.05); The image quality score and the excellent and good rate of image in group B were higher than those in group A and group C2 (P<0.05). Conclusion The scan triggering threshold technique, as commonly used scanning method in CT coronary angiography, to set the scan triggering threshold of dual-source CT at 130HU can obtain images of better quality, facilitate clinical observation and diagnosis,which is worthy of clinical promotion.