1. A system for multilevel simulation of an animation cloth, comprising: a computer for executing the following modules: a multilevel area generation module, dividing a plurality of grid units of the animation cloth into a plurality of level sub-areas based on a multilevel technique, wherein each of the level sub-areas is generated by dividing an upper level sub-area; a curvature calculation module, coupled to the multilevel area generation module, the curvature calculation module calculating a curvature of each of the level sub-areas in a first frame according to a plurality of first plane vectors of the grid units; a curvature comparison module, coupled to the curvature calculation module, the curvature comparison module comparing the curvatures of the level sub-areas with a flatness threshold; and a dynamic simulation module, coupled to the curvature comparison module, the dynamic simulation module calculating a second plane vector of each of the grid units in a second frame through different methods according to the comparison result of the curvature comparison module, wherein when the curvature comparison module determines that the curvatures of the level sub-areas are smaller than or equal to the flatness threshold, the dynamic simulation module calculates the second plane vector of each of the grid units on the boundaries of the level sub-areas through a physical simulation method and calculates the second plane vector of each of the grid units within the boundaries of the level sub-areas through an interpolation method, and the curvature comparison module stops comparing the curvatures of lower level sub-areas in the level sub-areas, and when the curvature comparison module determines that the curvatures of the level sub-areas are greater than the flatness threshold and the level sub-areas are on the lowest level, the dynamic simulation module calculates the second plane vector of each of the grid units in the level sub-areas through the physical simulation method.