为了将无衍射光应用于大景深成像系统中，分析了无衍射光束中心光斑的变化规律。利用菲涅耳衍射理论，讨论了无衍射成像系统中点光源在透镜焦点及焦点前后所产生的无衍射光斑形式。并根据准单色光理论，推导出准单色点光源在不同位置产生的中心光斑的尺寸和强度计算公式。最后，用红色高亮发光二极管作为准单色光源进行了验证实验。实验结果表明，无衍射光束中心光斑的半径随点光源距透镜距离的增大而减小，其强度随点光源距透镜距离的增大而增强。所得的结果为无衍射光应用于成像系统提供了理论依据。

In order to use non-diffracting beams to extend the depth-of-field of optical imaging systems,the variation rules of the central spot of non-diffracting beams were investigated. Based on the theory of Fresnel diffraction,the diffraction patterns were analyzed when the point source was placed in front of focal plane,at focal plane and behind focal plane. Then the radius and intensity calculation formula of the central spot of non-diffracting beams correspond to the distance from the point source to the lens or the distance between the partial coherent point source and the lens,were deduced according to the theory of partial coherent light. Finally,experiments were done by using a red high brightness LED as the quasi-monochromatic light source. The experimental results showed that the radius of the central spot decreased with the increase of the distance from the point source to the lens,and the intensity of the central spot increased with the increasing of the distance from the point source to the lens. The outcome provides stated academic gist to the applications of non-diffracting beams in imaging system.