In this paper, we discuss two types of vibrators, that connected by a single screw and that by a strain shell, respectively. The thick-end lengths of stepped horns are varied to find out their influence on the thin-end length, the gain of displacement amplitude, and the variation of displacement amplitude at the thin end. Optimized thick-end length are then selected out. For the vibrator connected by strain shell, the displacement amplitude of the thin end and the relationships among resonant frequencies and diameter of both the thick end and the thin end are determined. The relation between the thin-end length and resonant frequencies is also studied. The method for designing improved vibrators is given.