A local resonant phononic crystal model including four symmetrical vibrators was proposed. By changing the material components of the vibrator, this phononic crystal model could exist band gap and sound isolation peaks in different frequency range. In order to widen the frequency range of the sound isolation, a method was proposed to composite different structures. The structure plays a good sound isolation respectively in different frequency, and the composite structure can realize the widening of sound isolation range. The key factors affecting the sound isolation effect are studied through the finite element method. The results show that, the method can widen sound isolation range effectively, and the research provide an effective theoretical reference for wideband sound isolation of phononic crystals