Both the onedimensional and three-dimensional k-εturbulent models are used in this paper to simulate the flow in the shallow tailrace with a ratio 500∶1 of width to depth. Water surface profiles of 30 kinds of configuration are computed by one-dimensional model and velocity fields by threeX-dimensional k-εturbulence model. Sensitivity analysis on the effect of roughness of the bed is presented. Relying on above analysis,the shape of the tailwater channel is proposed, which is the most economical and can meet the design requirement. Furthermore, the three-dimensional k-εmodel is used to obtain the detailed velocity fields of the turbulence flows. The flow fields in the tailrace are analyzed on the different conditions of generating units operation. The resultsshow that the recommended program can meet the requirements of the enough submerged depth above the outlet of tail pipe with small discharge and the designed effective power head with large discharge. The recommended cunfiguration is also the most economical program.