3-D turbulent flow within 90° curved duct of square section is simulated numerically through Reynolds-averaged Navier-Stokes equations differentiated by the finite volume method. And three turbulent models, including standard k-ε two equation model, RNG k-ε model and Realizable k-ε model, are utilized to solve this problem respectively. The mathematic models and calculated results are given and compared with the experimental data. It is shown that turbulent flows within the core region and near-wall region of duct dominated by curved effects can be predicted accurately on the base of RNG k-ε model and two-layer zonal model.