Ecotechnology or ecological engineering is booming as a new water treatment technology in our country in recent decade for its advantages of high purification effects, low investment and easy operation. This article presented river mouth ecotechnology for purification of River Taoxi in Lake Erhai Basin. Through constructing a flooding weir at river mouth, River Taoxi water was intercepted into a purification system which was reconstructed by 9 abandoned fish ponds with total area of 550002 at left-side of river mouth. This purification system consists of 5 parts :1 )inflowing system consisting of constructed flooding weir and diversion wall;2)sand sedimentation system reconstructed by 4 ponds with an area of 27280 m² ;3 ) biological purification system reconstructed by 5 ponds with an area of 27720 m² which is designed to plant different life style aquatic plant;4) water flow distributing system which is responsible for long and uniformly water path and 5 ) outflowing system which is discontinuous gaps for water flowing out to Lake Erhai. The system has a design flow of 6.25 m³/s. It exerts purification effects for non-point pollution of River Taoxi mainly through sand sedimentation and plant purification. Water quality monitoring data in the operation period revealed that the system exert purification effects with TN removal rate of 55.2%-86.9%, TP removal rate of 76.4%-88.2%, SS removal rate of 29.4%-49.5%.