This Bifurcation angle (BA) has important predictive value for outcome of percutaneous coronary intervention (PCI) and the selection of interventional instruments and strategies. Therefore, bifurcation angle requires precise measurements. Intravascular optical coherence tomography (IVOCT) is the state-of-the-art high-resolution imaging modality which provides the possibility of the accurate measurements of bifurcation angle. However, to the best of our knowledge, there is no published work for calculating bifurcation angle based on IVOCT images. Inspired by previous studies on carotid bifurcation angle measurement based on black-blood magnetic resonance imaging, we creatively proposed a fully automatic computing method for bifurcation angle based on the detection of centers of the main vessel and side branch. Then, the detected center points are projected into a fitting plane by minimizing the reconstruction error to calculate the bifurcation angle. Finally, the 3D reconstructed main vessel and side branch demonstrate the proposed bifurcation angle calculation method is accessible. © 2017 IEEE.