The problem of particle motion in strained superlattices is transformed into a pendulum equation under multifrequency excitation using Fourier expansion. The stability of the system is discussed with Melnikov method and Lyapunov method, and the dual frequency excitation and single frequency excitation are analyzed in detail. The results show that the multifrequency excitation system can enter the chaos via the oddorder subharmonic bifurcation, and the system is stable when the damping coefficient is relatively large or the excitation intensity is relatively weak.