This paper summarizes the closure construction experience of border dike which is on deep soft soil foundation, and in open sea, deep water, 5 square kilometers reservoir area. The construction makes full use of the permeability of riprap dike and water thrown by large engineering ship, and using horizontal and vertical closure combined technology, heightening the bottom elevation and narrowing vertical width of closure gap. The construction technology not only reduces requirements of the rock size, but also reduces the risk and cost of closure construction.