An internal drum brake anti-falling device includes a carrier having an accommodating chamber and 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 comprises a base, mounted in the accommodating chamber, and a passive ring, mounted on the base. An outer diameter of the base defines a first ring surface configured in a concentric circle manner to the main shaft. An inner diameter of the passive ring defines a second ring surface, wherein an externally toothed ratchet teeth is arranged in a concentric circle manner on the second ring surface to allow the second ring surface and the first ring surface to be disposed opposite to and closely fitting to each other so as to allow the first ring surface and the second ring surface to sequentially generate maximum static friction force and kinetic friction force therebetween when the life belt drives the brake unit buckling with the ratchet teeth, so as to buffer the rotating drum and the life belt.