The utility model relates to an emergency braking device of a descending mine car. The mine car consists of a plurality of carriages hooked with each other; the rear part of the last carriage is fixedly connected with a steel wire rope of a winch; the top of the carriage is provided with fixed trolleys in a front-back symmetrical manner; grooves of the fixed trolleys are internally connected with a steel wire sling; two ends of the sling respectively extend to the front part and the rear part of the carriage; the rear end of the sling is fixedly connected with the steel wire rope of the winch; the front end of the sling droops from the front part of the carriage and is suspended and connected with a transverse stop lever, the length of which is approximately equal to a vertical distance between center lines of two tracks; two ends of the stop lever are symmetrically and perpendicularly connected with a downward clamping jaw capable of clamping into the tracks to prevent forwarding of the mine car; and two ends of the stop lever are respectively connected with an inclined stay cable which is diagonally pulled upward and fixedly connected with the sling. The emergency braking device of the descending mine car has a simple structure, can be used for emergently clamping the tracks, preventing continuous running of the winch and effectively guaranteeing safety of workers and facilities and has better practicability.