Recently, whispering-gallery modes in an optical microcavity gradually become an important area of research owing to its high quality factor, small mode volumes and on-chip characteristics. The cavity without circular symmetry, which is called asymmetric microcavity, is a significant branch of microcavity research. The asymmetric microcavity breaks rounded symmetry, so the cavity has directional radiation. It couples with external environment efficiently. It may be used in integrated optics and free space optical interconnects. We review the research progress of asymmetric microcavity, including directional emission of high collimation, efficient free space excitation, ratchet microcavity, and three-dimensional asymmetric microcavity. The basic principles and the prospect development are also outlined.