For small internal measurement requirement,effects of some parameter in the system,such as the detector pinhole size,the detector position,the numerical aperture and the amplification of the lens used and stray light,on the axial resolution were analysed.It is pointed that the effective detector pinhole size should less than 2.5,the precision micro displacement system should be used to make detector accurately fix position,the property of the axial deflection can be used to make differential confocal scanning microscopy,the large numerical aperture and the large amplification of the lens used will help to increase the axial resolution of the system,and the signal to noise ratio of the system can be improved by using polarized light.