A 3D small-field imaging system was established by using the fringe projection technique to measure the small objects having large slopes and/or discontinuous surface. A stereo microscope was used to generate a small-field projecting field and to capture the deformed fringe patterns on the measured small objects. Three fringe sets having the optimum fringe numbers were coded into one major color channel to generate color fringe patterns having the maximum fringe contrast of the captured fringe images. Through one channel of the stereo microscope, a Digital Light Processing(DLP) projector projected these generated color fringe pattern images onto the measured objects surface. From another channel, the fringe patterns were deformed with regard to the object surface and captured by a color CCD camera. The absolute phase of each pixel could be calculated from the captured fringe patterns by using the optimum three-fringe numbers selection method. The relationship between the absolute phase and depth was established to move a white plate to several known positions by using an accurate linear translating stage, so the 3D shape data of the measured objects were obtained. Experimental results on measuring 3D shape of small objects show the accuracy and availability of the developed 3D imaging system.