The semi-flow hot-compressed water treatment is expected as a promising technology to convert the lignocellulosics into energy and chemicals. When the lignocellulosics was treated by two-step semi-flow hot compressed water(1st stage: 230 degrees C/10 MPa/15 min, 2nd stage: 270 degrees C/10 MPa/15 min), its cell wall components can be effectively decomposed. In order to understand the decomposition behaviors of cell wall components, it is quite important to understand the chemical structure of each cell wall component. Thus, the cell wall structures and its chemical components of lignocellulosics were introduced, and for each component, the decomposition pathway were proposed. Furthermore, among the cell wall components, the lignin was confirmed not to be uniformly distributed within the cell wall. Therefore, an importance of the topochemistry of delignification was discussed.