In recently years, asymmetric evanescent coupling systems have become more and more important as silicon photonics is developing, because of the ultra-high index contrast and an ultra-small cross section of silicon nanophotonic waveguides. Asymmetric evanescent coupling systems on silicon have been developed successfully to enable ultra-small high-performance polarization-handling devices, special power splitting, as well as multi-channel mode conversion/(de)multiplexing. This paper will give a review for the recent progresses of asymmetric evanescent coupling systems on silicon.