针对管道测试的需求，将梯度折射率透镜的光学性能与显微镜相结合，设计了具有大景深的管道内窥镜光学系统.在保证所需放大倍率的同时，利用梯度折射率透镜介质折射率渐变的特点，使该系统的景深增大为原来的200倍.该系统像面近似球面的特点使其更适合圆形管道内壁的检测，当它与CCD等器件相结合，不仅实现管道内窥镜的数字化测试，而且能通过监视器在更大景深范围内、方便的监测管道内壁的裂痕、磨损等清晰的图像.

According to the test requirements of the inner wall of a pipeline, an optical system of pipeline endoscope is designed, which is based on particular optical feature of gradient index lens and microscope. The system has the advantage of large depth of field. In the condition of required magnification, the depth of field of the system is increased by 200 than the initial system, which is achieved by the radial gradient in the reflective index of gradient index lens. The system is more suitable for pipeline internal surface inspection based on the feature of the nearly spherical surface of image plane. Combined with CCD, the digitalization test of pipeline endoscope is realized. Clear image of the defects in the inner wall of a pipeline, such as the crack and abrasions, can be checked conveniently by monitor in a larger extant of depth of field.