In recent years, with the rapid development of coronary interventional techniques and the emergence of various new interventional devices, interventional treatment of selective unprotected left main bifurcation lesions has become an alternative treatment to coronary artery bypass grafting (CABG) to some extent. Interventional strategies for bifurcation lesions are mainly divided into single stenting and double stenting, and there are numerous interventional techniques and methods for double stenting, from the initial T stenting to the current TAP technique (T stenting and small protrusion technique), from Culotte, DK Culotte (double kissing Culotte) to DK mini Culotte, from classic Crush, Reverse Crush, Step Crush, Mini Crush to DK Crush, there is an extensive literature on the methods of these interventional techniques, so I will not go into details here. However, in general, stenting of left main bifurcation lesions remains a difficult interventional problem with a high risk of intraoperative complications due to acute occlusion or near occlusion of the side branch, and a high rate of postoperative major adverse cardiac events (MACE) and target lesion revascularization due to in-stent thrombosis or restenosis of the side branch opening. In recent years, with the development and application of intravascular imaging and functional examinations, IVUS and FFR assessment have shown great value in guiding the application of interventional strategy development and long-term prediction for left main trunk bifurcation lesions. I. The guiding role of IVUS in the interventional treatment of left main trunk bifurcation lesions. IVUS can provide a cross-sectional image of the vessel, not only to observe the lumen morphology, but also to observe the structure of the vessel wall and directly visualize the lesion located on the vessel wall. Prior to intervention of left main bifurcation lesions, IVUS can accurately assess the plaque distribution at the bifurcation site and directly measure the MLA/MLD at the branch openings and LM ends to guide the choice of balloon and stent diameters as well as the procedure. Current evidence-based medicine has found that a single-stent technique can be used when the lumen area of the LCX opening is greater than 4 mm2 or when the plaque load is ≤60%; also, IVUS can accurately evaluate the degree of plaque calcification and apply cutting balloons and rotary grinding to pretreat the lesion in a timely manner if 360° annular calcification is present to obtain the best stenting results. After stenting of left main trunk bifurcation lesions, IVUS can accurately evaluate the post-stenting apposition status and degree of lesion coverage for optimal stenting. It is currently believed that post-stenting expansion is necessary for LM MLA <8.5 mm2?or LAD/LCX MLA <5.5 mm2; in addition, IVUS can assess the reduction in branch opening area due to plaque and ridge displacement at the bifurcation site after stenting, and several studies have shown that the branch opening is the site with the highest incidence of restenosis after DES implantation, regardless of the chosen procedure, and The MLA after PCI was the main determinant; after single-stent implantation, the percentage of branch-opening restenosis was much lower in those with MLA >4.0 mm2 at the LCX opening than in those with MLA ≤4.0 mm2. Similarly, after double stenting, the proportion of branch-opening restenosis was much higher in those with MLA ≤5.5 mm2 at the LCX opening than in those with MLA >5.5 mm2. Large-scale evidence-based medicine is still needed to determine whether interventions for IVUS-guided bifurcation lesions can improve long-term prognosis, but the current consensus still recommends the routine application of IVUS for left main bifurcation lesions. II. The guiding role of FFR in interventions for left main bifurcation lesions. FFR is the “gold standard” for functional assessment of coronary artery stenosis, and its accuracy is much higher than that of noninvasive functional tests. In the intervention of left main bifurcation lesions, FFR can provide information that is not available in IVUS and can guide the best interventional strategy. Prior to intervention for left main trunk bifurcation lesions, FFR values are measured at the branch vessel opening and LM distal stenosis, respectively, to initially guide the stenting strategy, single or double stenting. It must be noted, however, that because stenosis at the end of the LM affects the FFR value of the branch opening, which is increased after stenting of the LM in some lesions, the decision to intervene in the branch vessel cannot be based solely on the preoperative FFR value of the branch, but must be measured again after LM stenting to decide whether intervention is necessary. On the other hand, LAD or LCX stenosis can lead to an underestimation of the severity of LM stenosis, and when the LAD or LCX stenosis is lifted, the FFR value of the LM also decreases, so the FFR value of the LM must be measured again after the branch stenosis is lifted to decide whether stent implantation is necessary to avoid missing important lesions. In addition, when we select a single stent implantation in the main branch vessel, the opening of the unintervened vessel (often the gyral branch) is often found to be compressed on the imaging and severe stenosis is visible. In fact, there is often a large inconsistency between the imaging assessment and the functional assessment, and at this point, the FFR provides a great guidance on whether we should intervene in the gyral branch opening, and in branch vessels with branch openings greater than 50% stenosis In 74% of the branch vessels with branch openings greater than 50% stenosis, the FFR was greater than 0.80. This indicates that the severity of branch vessel lesions may be overestimated by common coronary angiographic findings, leading to excessive branch vessel interventions, and the application of FFR can effectively guide the reasonable disposition of branch lesions. Third, the application of FFR and IVUS in the interventional treatment of left main trunk bifurcation lesions is recommended: FFR can accurately assess the functional significance of the lesion, while IVUS can provide a comprehensive understanding of the anatomical values of lesion plaque load, plaque composition, lumen area, and stent apposition to the wall, etc. Because the accuracy of the assessment of left main trunk bifurcation lesions by imaging results is limited, the application of FFR and IVUS is highly recommended To assess the severity of the left main bifurcation lesion and to develop the best treatment strategy in conjunction with the patient’s clinical features, and to guide the cardiovascular interventionalist to manage the left main bifurcation lesion more comfortably and confidently.