Mitral regurgitation is one of the most common heart valve diseases. Transcatheter edge-to-edge repair (TEER) is currently the most developed and commonly used interventional technique for mitral regurgitation and is recommended by the latest European and American guidelines for patients who are at high surgical risk. TEER device usually consists of a clamping device and a delivery system. The trajectory of the clamping device is called the trajectory, and the trajectory can be well established with the five dimensions movement of the delivery system: left-right oscillation, anterior-posterior oscillation, overall parallel movement, the clamping device's own clockwise rotation, and vertical up-and-down movement. The delivery system's anteroposterior and lateral oscillations are concentrated on the virtual puncture site. Furthermore, the location of the septal puncture site has a significant impact on the establishemnt of the trajectory. The evulation of three variables and adherence to the "4M principles" are necessary for the successful TEER. The three variables are: the position of the clip in the center of the regurgitation,the arm orientation of the clip perpendicular to the boundary of anterior and posterior leaflets, as well as the appropriate length of clamping. The "4M principles" include favorable valve morphology, residual mitral regurgitation below grade 2+, mean transvalvular pressure≤5 mm Hg, and an appropriate amount of leaflets clamping. Patients' baseline situation, the degree of mitral regurgitation and ventricular remodeling, as well as the valve morphology and the outcome of the procedure, are the factors determining the prognosis of patients after TEER.