The invention discloses an assembling mechanism for a key cylinder marble inverted installing machine, and relates to the technical field of key cylinder assembling. The assembling mechanism comprisesa base, a first feeding assembly, a second feeding assembly and an installing base; the first feeding assembly is located on the installing base; a first contact pin is arranged on the base, used forpushing an upper marble and a spring which are arranged on the first feeding assembly into the second feeding assembly and located on the first feeding assembly; the second feeding assembly is located on one side of the installing base and slidably connected with the base; and the installing base is slidably connected with the base. According to the assembling mechanism for the key cylinder marble inverted installing machine, by installing the first feeding assembly and the second feeding assembly, automatic conveying and assembling of the upper marble and the spring are achieved, the automation degree of the assembling process is improved, the assembling efficiency is improved, and the production cost is reduced.