The transition region between the neighboring ecosystems was called ecotone. In view of global ecology and landscape ecology, ecotone may be divided into four kinds: terrestrial ecotone, inland water-land ecotone, marine-land ecotone and marine ecotone. The marine ecotone was presented and defined as the transition region between the neighboring marine ecosystems according to the ecotone theory. The main research fields are as following:to build the criteria of marine ecotone, such as biodiversity index or other ecological indexes, three dimensional structures of marine ecotone,  the ecological function of marine ecotone, the sensitive elements and responsive mechanics of marine ecotone to global change,the maintaining biodiversity mechanics in marine ecotone, the relationship between marine ecotone and form of fishery field. The difference between marine ecotone and terrest rial ecotone and marine front were discussed. The marine ecotone field will become one new “growth point”in marine ecology.