Abstract: The SBR is applied for mode-locking in the femtosecond solid-state lasers to obtain the steady mode-locked pulses.In this paper,the structure and the spectrum of the saturable Bragg reflector are generalized in detail,and the relation between the absorption coefficient,saturation intensity and the inherent parameters of the SBR is derived from the density matrix equations.The basic mode-locked mechanism of the SBR has been analyzed and the fundamental mode-locked conditions of SBR in the solid-state lasers has been obtained.It is found that the SBR can be used in the mode-locking of the femtosecond solid-state lasers and it can enhance the properties of mode-locked pulses.