Aim To discuss optimal reconstruction phase of 16-slice CT coronary angiography.Methods 136 patients with suspected or diagnosed coronary artery disease were studied with 16-slice spiral CT.Choosing left and right coronary artery in the axial enhancement scanning images,previewing 10 images at 0%-100% of the cardiocycle in increments of 10%,We evaluated grade of the image quality and number of the ratable coronary artery in different reconstruction phases.We selected the most clear image of left and right coronary artery,and recorded the phase.Raw data were reconstructed with thin images at the best phase.All images were reconstructed in the mode of maximum intensity projection(MIP),multi-plane reformation(MPR),curved planar reformation(CPR) and volume rendering(VR).Results Three coronary,the left anterior descending(LAD),the left circumflex(LCX) and the right coronary artery(RCA),segments were analyzed in each patient with regard to image quality.There was significance of difference in the number of the ratable coronary artery in different reconstruction phases(χ2=34.14,p<0.05).The number of good image in coronary arteries displayed by 40%,50%,70%,80% and the rest reconstruction phases had significant difference(p<0.05).The optimal reconstruction phase of RCA,LAD and LCX were 80% and 70% of the cardiac cycle.The second phase was 40% and 50% R-R phases.Conclusions Image reconstruction in the optimal phase can decrease the artifacts of cardiac motion as possible and improve the quality of images and raise work efficiency obviously.