With the help of microcomputer, this paper introduces and realizes the flood algorithm, which can convert vector data to object- centred run length encoding rapidly and store it conveniently. The object-centred run length encoding has following advantages: Less memory, Higher operating speed, Doing many algebraic and logic operations. In a word, it has advantages of both vector data and raster data. Finally, the principles mentioned above were applied to forest site information management system for the coastal zone in Dongtai, Jiangsu, the satisfying results were acquired.