Abstract: In order to meet the requirements of high voltage DC circuit breaker for the fast operation mechanism and high voltage level, a new electromagnetic repulsion mechanism for 126 kV vacuum circuit breaker is designed for long strokes with high breaking and closing speeds. It consists of a double-coil and a solenoidal electromagnetic repulsion mechanism connected in series. Firstly, electromagnetic force simulations are carried out using the finite element method. The feasibility of the mechanism is initially verified by analyzing its electromagnetic repulsion and displacement/time characteristics. Then, the single-variable method is used to simulate and analyze its motion characteristics. The interaction of the mechanism and the design principles for parameter optimization are obtained. Finally, the electromagnetic buffer is designed to reduce the bouncing of the break. The effects of buffer drive circuit parameters and buffer input time on buffer characteristics are analyzed. The study shows that the electromagnetic repulsion mechanism has the characteristics of large rigid separation speed, long acceleration time, and suitable for long stroke drive. The designed electromagnetic repulsion mechanism has a short full-stroke opening time, only 5.41 ms, with the cooperation of the parameter groups of 3500 μF and 1200 V for the breaking capacitor and 3500 μF and 1800 V for the buffer capacitor.