A speed governor assembly and an elevator system. The speed governor assembly includes: a sheave; a centrifugal mechanism mounted on the sheave and rotating together with the sheave; an overspeed protection switch at a first distance from a radial outer side of the centrifugal mechanism; a core ring disposed coaxially with the sheave; and a triggering arm rotating together with the core ring; wherein the centrifugal mechanism engages with the core ring and drives the core ring and the triggering arm to rotate when the sheave reaches a second speed, and the rotation of the triggering arm can contact and trigger the overspeed protection switch.