Abstract: In the new spread model for forest fire, bitmaps are operated and outlines of images are searched at the basis of the metagraphic set of fire-area shapes and the gray level image for spread calculation. Complex topological relations among geographical elements are solved with the scan-line flood-fill algorithms. The projection transition of the fire-area shape is replaced by a combined graphical transformation of rotation and shear. And the solar radiations are calculated by means of the gray level image of terrains. Thus the limitation on computational performances of the original wave propagation spread model is overcome. The essence of computational acceleration making use of computer graphic techniques is analyzed primarily. A calculation case is presented in order to show that the new spread model can provide forest fire management with precise, reliable, overall, maintainable and adaptable diagram of fire development in real time.