Minimized probe is a common requirement in endoscopic optical coherence tomography (OCT). We introduce the development of mainstream designs based on ball lens, fiber lens, graded index fiber, free form lens and free-lens, summarize their advantages and disadvantages, and put forward some suggestions for miniaturization of the probe. The development of probe with extended depth of focus (DOF) poses significance on imaging subcellular structure of human internal organs. We review several important techniques of DOF extension suitable for miniature probes, among which the probe based on mode interference is believed to have great potential because of its easy fabrication, compact structure, high light transmission efficiency, optimized working distance and DOF, and uniformity of axial light intensity.