Abstract: An improved region partitioning algorithm is presented and applied to virtual machining for increasing simulation speed.By the algorithm,the display surface is first divided into small regions.Then the triangular facets are regrouped according to their covering regions.During machining simulation,since only the facets of modified regions need to be redrawn,each frame can be rendered in a short time.Three important aspects of the algorithm：region judgment of triangular facets,traversal of virtual scene components and redrawing region judgment are discussed in detail.The algorithm is validated in Virtual Machining System （VMS） and tests are made to demonstrate how the region granularity can affect the performance of the algorithm.