The present invention relates to a bone conduction speaker and its compound vibration device. The compound vibration device comprises a vibration conductive plate and a vibration board, the vibration conductive plate is set to be the first torus, where at least two first rods inside it converge to its center; the vibration board is set as the second torus, where at least two second rods inside it converge to its center. The vibration conductive plate is fixed with the vibration board; the first torus is fixed on a magnetic system, and the second torus comprises a fixed voice coil, which is driven by the magnetic system. The bone conduction speaker in the present invention and its compound vibration device adopt the fixed vibration conductive plate and vibration board, making the technique simpler with a lower cost; because the two adjustable parts in the compound vibration device can adjust both low frequency and high frequency area, the frequency response obtained is flatter and the sound is broader.