Abstract:Slightly-off-axis interferometry theory is introduced and the angle between the object and sample path is calculated via the auto-correlation(cross-correlation) theory.According to this special angle,the optimized fringe spacing is introduced.The slightly-off-axis interference system is compared with on-axis and off-axis interferometry,which is good for high resolution.It is concluded that the biological cells with different size should choose the proper micro objective.As a result,it is convenient for the experiment operating and the enhancement of the phase reconstruction accuracy.The above results shed more lights on novel interferometry.