The invention relates to a method for ecologically improving the water quality of a water delivery type lake. In the method, frame outlines of water-permeable diversion piers, water-permeable spur dikes and water-permeable diversion walls are respectively formed in the lake; rubbles are arranged outside wood piles; gabions are arranged on the inner sides of the wood piles; gravels are filled among the gabions to form the water-permeable diversion piers, the water-permeable diversion walls and the water-permeable spur dikes; the water-permeable diversion piers are arranged at an inlet of the lake; and the water-permeable spur dikes and the water-permeable diversion walls are continuously staggered along the direction of water current. According to the method, the defects that the engineering quantity is large, the treatment expense is high, secondary pollution is easily caused, the symptoms not the causes are addressed, and the like are overcome; the water-permeable diversion piers, the water-permeable spur dikes, the water-permeable spur dikes and the water-permeable diversion walls are sequentially arranged in the lake, so that a water body in the lake is fully exchanged, the hydraulic retention time is prolonged, the water quality purification is enhanced, the silt settling effect is improved and the flow speed is reduced; the method can be used for creating environments which are more suitable for organisms to live in, enriching species and facilitating the recovery of a biological system; and the method has the advantages of simpleness for operation, convenience for construction, stable functions and low construction cost.