Abstract: Water age is the time for water replaced by that from outside. Water age plays an important role in algal bloom in reservoirs and is taken as an ideal tracer which can describe water mixing rate and process. It can yield very effective diagnoses, for example the characterization of the mixing and renewal of water masses, of the fate and mixing of contaminants. In the research, an age simulation method based on dyeing simulation was developed to improve EFDC model. Taking Taicang Second Water Plant reservoir pump house location optimization as an example, reservoir circulating currents and water age were modeled to reduce the water age in order to reduce algal bloom risk. Since the air temperature, water depth and nitrogen and phosphor input are hard to control, to optimize the water age and the cycling currents of reservoir by water intake pump house location optimization is one of the most useful ways to control the risk of algal bloom in reservoir by changing growth inhibition.