The invention provides a prefabricated member for promoting development of laminar flow to turbulent flow and a using method.The prefabticated member is composed of a plurality of monomers, each monomer is composed of a monomer body, a hollowed-out portion, a spoke portion and a connection hole, the cross section of each monomer is in a regular octagon shape and is composed of an outer edge regular octagon, a middle regular octagon and an inner edge regular octagon, and the two octagons constituted by each middle regular octagon and the corresponding inner edge regular octagon are sections of the hollowed-out portions.The prefabricated member changes the laminar condition of a river, the turbulent flow forming probability is increased, water potential energy is increased through backwater and converted to water backwater, the reoxygenation speed of dissolved oxygen in the river is increased, the water self-purification process is promoted, and water environment quality of water is enhanced.