In this paper, the simulations of the three-di-mensional turbulent flows through hydraulic turbine compo-nents[1] were conducted based on the standard k-ε turbulentmodel with body-fitted coordinates and staggering grid sys-tem. The SIMPLEC algorithm was adopted in the numericalprocedure. A new method to treat the periodic boundary con-dition was used. The calculated results of the new methodwere compared with those of traditional ones. These resultsindicate that the new method can give much better results,and can be used in simulating flow through rotational impel-lers. The presented method can be combined with alternativeturbulent model or employed in large eddy simulation.