The rapid growth of multi-media and data applications has driven the bandwidth demand for long-haul fiber-optic links at unprecedented rates. Against this background, the combination of time division multiplexing, wavelength division multiplexing, and polarization division multiplexing with multilevel modulation makes the transmission capacity of single-mode fibers in the large-capacity transmission system rapidly approach the Shannon limit. In view of this problem, the space division multiplexing (SDM) technology that can break through this limit provides new solutions for the growth of fiber capacity in the future. In this paper, we discuss three kinds of SDM fibers, namely, multi-core fiber, few-mode/multi-mode fiber and few-mode multi-core fiber, and introduce the research progress and design method of the SDM fibers. Furthermore, the comparison among the above SDM fibers is also discussed to reveal their advantages and disadvantages.