The development of landforms at different spatial scales essentially belongs to the problem of gravity geomorphological evolution characterized by perilous rocks, landslides, and debris flows. Paying attention to two classic geomorphic function of “leveling” and “accumulation”, a nested-loop evolution theory for gravitational geomorphology has been preliminarily proposed through integrating the three famous geomorphological evolution theories of Davis, Penck, and King by introducing geotechnical mechanics and applied mechanics. Following the new theory, during stable period of tectonic movement, regional geomorphological evolution involves a composite structure of “macro scale gradual change effect loop”, “micro scale gradual change effect loop”, and “rapid change effect loop” of gravity geomorphological processes. Based on the theory, the “three-loop” effect of gravity geomorphology process is analyzed, and the time scales of macro scale gradual change effect with tens of thousands of years, micro scale gradual change effect with years to hundreds of years, and rapid change effect loop with minutes to hours are given. Some scientific attributes of the new theory are discussed, reminding of a methodology and practical approach for gravity geomorphological disaster reduction, which answers the question of “What is gravity geomorphology and how is it”. Further, a new idea of gravity geomorphological disaster reduction combining “process containment” and “impact direction steering” has been proposed, with “evolution” as the guiding principle and “process” as the objective. The theory enriches the scientific contents of traditional geomorphology and has positive significance for promoting the disaster reduction of gravity geomorphology in engineering.