Objective To investigate the value of low tube current combined with narrow window and iterative reconstruction in reducing radiation dose of coronary CT angiography. Methods 80 patients with suspected coronary heart disease were randomly divided into two groups: group A and group B, 40 patients in each group were treated with CCTA. Group A had 120 kV scan tube voltage, intelligent milliampere tube current and scan window 30%-80% of cardiac cycle. Group B had 120 kV scan tube voltage, 75% of intelligent milliampere tube current and scan window 70%-80% of cardiac cycle. Group A was reconstructed by filtering back projection (FBP) and iterative reconstruction (IR) to obtain AF and AI. Group B was reconstructed by IR. The noise, signal-to-noise ratio (SNR), subjective image quality (score) and radiation dose (ED) of the three groups were compared. Results Noise in AI, B and AF groups increased and SNR decreased in turn. There was statistical significance in noise and SNR between AF group and AI and B group (P<0.05). Subjective image quality evaluation showed that AI group was better than other two groups (P<0.05), AF group was the worst, and there was no statistical significance between AF group and B group (P>0.05). EDs in A and B groups were (3.40±1.34) mSv and (1.26±0.61) mSv, respectively, with statistical difference (P<0.05). Conclusion Low tube current combined with narrow window and iterative reconstruction can reduce the radiation dose of CCTA without reducing the quality of coronary artery imaging.