The effect parameters,such as fiber optical spot size,the numerical aperture and magnification of a gradient index lens,match and assembly between a gradient index lens and the fiber on axial resolution of the fiber optical confocal microscope.It is pointed that,in order to obtain high axial resolution,parameter A related to fiber optical spot should be less than 3,the high magnification gradient index lens should be selected,the numerical aperture a gradient index lens should less than that of a fiber,and precision assembly between a gradient index lens and the fiber should be abtained.