The invention discloses an ecological submerged dam system for urban landscape rivers and a construction method. The ecological submerged dam system comprises a submerged dam, an absorption basin, a water truck, submerged plants and a sludge discharge tank, wherein the absorption basin comprises an apron and a tail-weir; and the submerged dam and the absorption basin are constructed from bio-film forming stone net cages. Water falling from the dam top drives the water truck to rotate, and water in the absorption basin is continuously rolled up and drops, so that the water is fully doped with gas dissolved oxygen along the way, bio-film decomposition of eutrophic substances in the water is facilitated, and the produced sludge automatically converges into the sludge discharge tank so as to be discharged; and the residual eutrophic substances in the water are absorbed by the submerged plants at the tail-weir, and the water body is further purified. The construction method comprises the following steps: 1, cleaning the riverbed; 2, manufacturing the bio-film forming stone net cages; and 3, performing field installation and fixation. The discharged water is driven to be automatically doped with gas dissolved oxygen, the river water is continuously purified by adopting a bio-film process, phytoremediation and other ecological technologies, and the ecological submerged dam system has the advantages of being excellent in water purification effect, ecologically attractive, simple in construction, convenient to maintain, low in cost and the like.