The delimitation of the continental shelf and exclusive economic zone has been based on that of the territorial sea. The baseline of territorial sea determined the breath of territorial sea and thus the external boundary of adjacent zone, exclusive economic zone and continental shelf. But the determination of baseline is dependent on the choice of base points. The connecting of various base points and forming a baseline has been one of the basic methods. The influence of island in the determination of base points has been an issue to be resolved.In 1982, Convention on the Law of the Sea established an imperfect system of island and there is no provision of validity of island in the delimitation of sea. Therefore such international judiciary institutions as International Court of Justice has developed the content of island regime through cases and almost formed a doctrine of full validity, semi-validity, and no validity for island. The disputed sea area of the mouth of Beibu Gulf, East Sea, and South China Sea has to be delimitated peacefully in accordance with international law rules about delimitation of sea area with consideration of those special circumstances in individual cases.