To meet the needs for new fiber optic sensors,the process for fabricating 3D microstructures in silica fiber materials by femtosecond laser is discussed.Experimental results show that the ablation threshold of fiber is about 1.5 J/cm2;the ablation depth is of approximately linear relation with the laser energy.Under some conditions,the higher energy is more beneficial to the formation of upright hole.The formation mechanisms of taper hole,upright hole and their surface morphology are discussed.The disintegration appeared on the back surface of the optic fiber is analyzed.Some three-dimensional microstructures were fabricated on the fiber end,such as F-P cavity,cantilever structure,etc.