The recursion and iterative algorithms of source flood submerge area would take too much computer resource, and when the recursion depth is deep, the system would often collapse because of the system stack overflow. To deal with this problem, this paper proposes a source flood submerge model and the related algorithm based on DEM, on the condition of the given water level of the flood. A "seed spreading" algorithm for visiting every node of the stack is developed. First of all, a new empty submerged buffer stack is created, and from the flood source point, it is determined whether the source point's flood level is lower than the given water level. If it is true, the source point is put into the buffer stack and is marked as the submerged grid. Then the surrounding 8 neighborhood raster grids are searched, if a grid meets the condition, we put the grid into the flooded area buffer stack. At the same time, the first element of the stack is popped up. Repeat this operation until the flood buffer stack is empty, and extend this operation to all nodes of the stack, just like the "seed spreading" and eventually complete the inundated area calculation. Compared with the original recursion algorithm, this algorithm has improved the calculation efficiency and stability to a some extent. This algorithm was successfully applied in the "Nanchang flood submerge analysis system".