The invention relates to a high-speed opening operation mechanism of a middle-and-low-voltage direct-current circuit breaker, which is particularly suitable to be applied to high-speed direct-current circuit breakers with high requirements on short-circuit breaking capacity. The operation mechanism comprises a moving contact, a fixed contact, a closing retaining device and an electromagnetic repulsion mechanism, wherein the closing retaining device comprises a closing retaining spring, a horizontal limit sleeve and a closing retaining top-block; and the electromagnetic repulsion mechanism comprises an opening push-rod, a reset spring, a repulsion disc, a coil, a charge and discharge circuit and a controller. The invention provides a high-speed opening operation mechanism of a middle-and-low-voltage direct-current circuit breaker, which is simple in structure, easy to operate, and quick in opening speed; and by using the operation mechanism, the on-off speed of the direct-current circuit breaker can be improved, the dead time of an electric arc can be shortened, the ablation of the contacts is reduced, and a situation that the electric arc enters into an arc extinguish chamber as soon as possible and then is extinguished quickly is facilitated, thereby improving the on-off performance of the direct-current circuit breaker.