The invention provides a saturation absorber for passive mode-locking of fiber lasers, comprises a SiC crystal substrate, a graphene layer grown on one surface of the SiC crystal substrate and a spherical face with R radius of curvature ground and polished on the other surface of the SiC crystal substrate. The SiC crystal substrate is fixed in a mechanical clamp; two ends of the clamp are reserved for circular light through holes for optical fiber heads to be connected with.