Abstract: Focusing on the rotating motion and vortex flow of rotors, a dual grid modelling method is discussed, in which body fitted moving structured grids are used to capture the boundary layer flow and background grids with adaptive mesh refinement (AMR) are used for the blade tip vortex flow. A method of generating block structured Cartesian grids is developed, in which the grid refinement or coarsening is performed on blocks with identical grid dimensions. All Cartesian blocks are organized by the octree data structure and spatial filling Z curves, which meets the requirements of adaptive refinement and parallel partition. The dual grid method is applied for the UH-60A rotor simulation. The initial Cartesian background grid is automatically generated with the body fitted blade grid as the input. For rotor flows in hovering and forward flight conditions, the Landgrebe and Beddoes wake models are introduced respectively to adaptively refine the background grids. The maximum allowed number of grid layer is 9 and the grid spacing for the tip vortex filament in the target area is 1% of the chord length. Results show that the present Cartesian grid adaptive method is able to flexibly refine or coarsen grids for the blade tip vortex by controlling the maximum refinement level, the size and grid spacing of the target refinement area for the vortex capturing. The present AMR method is highly efficient in grid adjustment, and shows convincing prospects in improving the simulation accuracy of unsteady blade tip vortices.