The Ludao Lake with an area of 0.86 km2 and 50% water surface ratio, was taken as an example to study the eco-hydraulics techniques for preventing lake eutrophication. Besides extal water inflow and outflow, the term related to intal local flow circulation was added in the continuity equation of two-dimensional horizontal hydrodynamic model, and further the hydrodynamic model was calibrated by the scenario of no water exchange. The velocity of 0.2 m/s was suggested to be the critical velocity of controlling algal bloom. To achieve the critical velocity in the whole lake, three factors were analyzed, which are wind, artificial extal inflow augmentation and intal local flow disturbance by pump circulation. It is found that the role of wind can be disregarded. For the eco-hydraulics technique of extal lake water inflow augmentation, the water flowing route should be firstly optimized, further, the lake inflow has a critical value under specified water level due to the narrow inlets, so the whole lake is difficult to reach the critical velocity to prevent algal bloom, and a combination of extal inflow augmentation and intal local flowing disturbance should be considered. Simulation results show that the combination of extal water inflow augmentation and intal local flow disturbance requires less eco-flow to achieve the global critical velocity than the sole intal local flow disturbance, for the Ludao Lake, the former requires total eco-flow of 25 m3/s, which reduces by 50% than the latter requiring total eco-flow of 52 m3/s.