A parallel Navier-Stokes solver based on dynamic overset unstructured grids method is developed to simulate the unsteady turbulent flow field around helicopter in forward flight.The present method has the advantages of unstructured grid and Chimera grid and is suitable to deal with multiple bodies in relatively moving.Unsteady Navier-Stokes equations are solved on overset unstructured grids by an explicit dual time-stepping, finite volume method.Preconditioning method applied to inner iteration of the dual time-stepping is used to accelerate the solution of the governing equation.