An external drum brake anti-falling device includes a carrier having an accommodating chamber and a main shaft crossingly arranged in the accommodating chamber for supporting a rotating drum to autorotate, wherein the rotating drum has a life belt coiled thereon, a brake unit arranged at an end thereof, and a drum brake module, which includes a base, mounted in the accommodating chamber, and a passive ring, mounted on the base. The base has a through hole axially and penetratingly arranged thereon and a slit communicating an inside and outside of said through hole. The wall surface of the through hole is a first ring surface. An outer diameter of the passive ring is a second ring surface. The passive ring has internally ratchet teeth arranged therein. when the life belt drives the brake unit to be engaged with the ratchet teeth, thereby buffering the rotating drum and the life belt.