Objective To compare and analyze the effects of 256 slice spiral CT prospective and retrospective ECG gating technique on coronary imaging quality and radiation dose. Methods 70 cases of patients who were diagnosed with suspected coronary artery diseases in our hospital between January 2013 and December 2015 were divided into prospective gating group (36 cases) and retrospective gating group (34 cases) by randomized double blind method. The control heart rates of all patients before examination were < 75 times /min. The average radiation time, effective radiation dose and coronary imaging quality were compared between the 2 groups. Results The excellent rate of coronary imaging quality in prospective gating group (59.2%) was significantly higher than that in the retrospective gating group (51.1%) (P<0.05) but there was no significant difference in good and excellent rate of coronary imaging quality between the 2 groups (90.3% vs 91.1%) (P>0.05). The average radiation time and effective radiation dose of the prospective gating group [(3.42±0.20)s, (3.15±1.00)mGy was significantly less than that of the retrospective gating group [(5.22±0.38)s, (9.67±3.52) mGy] (P<0.001). Conclusion The coronary imaging quality of 256 slice CT prospective and retrospective ECG gating technique is high and compared with retrospective gating technique, the prospective gating technique can significantly reduce the radiation dose.