In order to solve the problems that the efficiency is low when the segment of three-dimensional Computed Tomography Angiography (CTA) coronary arteries images with complex structure and small region of interest, a segmentation algorithm combining region growing and graph cut was proposed. Firstly, a method of region growing based on threshold was used to divide images into several regions, which removed irrelevant pixels and simplified structure and protruded regions of interest. Afterwards, according to grey and space information, simplified images were constructed as a network diagram. Finally, network diagram was segmented with theory of graph cut, so the segmentation image of coronary arteries was got. The experimental results show that, compared with traditional graph cut, the increment for the segmentation efficiency is about 51.7%, which reduces the computational complexity. On the aspect of rendering quality, target areas for segmentation images of coronary arteries is complete, which is helpful for doctors to analyze the lesion correctly.