Abstract: Synthesizing the main ideas of regular grid modelling and free-space modelling, a structure basedfree-grid method is proposed to definitively the overcome opationality of imaginary boundaries generation in the process of free-space segmentation according to environment structural data and hence theuncertainty of the path is eliminated. Furthermore, the structure based free-grid model can be used toavoid'making a big detour, during the path planning to some extent.