Abstract: Abstract:On the issue of delimitation of the continental shelf in East China Sea and exclusive economic zone , Japan stuck to break the principle of natural prolongation ,urged the principle of midline. This paper will give a perspective of physical geography ,demonstrates OKINAWA trough is natural boundary of continental shelf in East China Sea.And combining with international law,discussion?on?the benefit of complying with the?fairness?principle in the?delimitation of the continental shelf,?and?abiding by the?fairness?principle?is that made the?principle of "natural prolongation"?as?the main consideration?.