In this paper, the theory of linear stability analysis is used in analyzing the complex amplitude of vibration of multi-photon optical bistability which was described by semiolassical Maxwell-Blooh equations. The results of analysis show that after the adiabatio elimination being acted to atomic polarization there is no instability on cooperation branch and one single branch of multi-photon optical bistability characteristic, showing that there is no chaos of multi-photon optical bistability which was caused by the instability of the soft mode at the same time. It has been indicated that the third condition of stability is related to bistable characteristic of umlti-photon optical bistability.