A fast mechanical switch using an electromagnetic repulsion mechanism has broad applications in fields such as power system fault current limiting, power quality control, and for a phase-controlled switch. To improve the breaking capacity of the circuit breaker, a new fast mechanical switch with a double mechanism is designed, one which combines the advantages of a spring operating mechanism and an electromagnetic repulsion mechanism. The presented switch ensures the reliability of breaking and also realizes three-phase split-phase phase-controlled rapid breaking. From its working principle, the calculation equation of the electromagnetic repulsion mechanism is deduced, and a three-dimensional finite element model of the mechanism is established. In addition, the corresponding field-path coupling dynamic characteristics are analyzed. The influence laws of different mechanism parameters on the current and electromagnetic repulsion are also analyzed. The guiding principles for the design of a fast mechanical switch are given. Combined with the structural strength simulation analysis of key parts, the prototype design of a new fast mechanical switch is completed. The experimental results show that the full breaking time of the new fast mechanical switch is 15.5 ms, which verifies the correctness and reliability of the design scheme.