A class of single-degree-of-freedom piecewise smooth mechanical vibration systems was studied. The modes and distribution regions of sub-harmonic vibrations in the two-parameter plane are numerically calculated. The bifurcation characteristics, stability and transmigration laws of sub-harmonic vibrations in the sub-harmonic inclusion regions are investigated in detail by using the continuation shooting method. The results show that the grazing bifurcation is continuous in the elastic impact system. In the sub-harmonic inclusion regions, PD-type grazing bifurcation are prevalent, and SN-type grazing bifurcation and subcritical period-doubling bifurcation cause jumps and hysteresis phenomenon of system response. Multiple attractors coexist in the high-frequency subharmonic inclusion regions, and the chaotic attractor ends up at the boundary crisis.