The invention discloses a loading guide rail mechanism for a horizontal loading device, and belongs to the technical field of horizontal loading. The technical problems caused by original loading structural space and a loading guide rail scheme are solved. The loading guide rail mechanism for the horizontal loading device comprises a trolley frame, moving surface bearings, a device body frame, a trolley guide warp-preventing mechanism, a hydraulic cylinder, a loading guide rail, cylinder moving bearings, cylinder guide bearings, a missile pushing trolley drive pin, and a drive pin hole base of the hydraulic cylinder; through restraint of the cylinder moving bearings and the cylinder guide bearings installed on the hydraulic cylinder, the hydraulic cylinder can linearly move on the integrated loading guide rail in a reciprocating mode; meanwhile, the hydraulic cylinder directly drives a loading missile pushing trolley frame to synchronously move through the missile pushing trolley drive pin, so that the loading system operates stably and is reliable in performance; and the system is convenient to implement, use and maintain, and the manual emergency loading mode implementation can be achieved rapidly.