Abstract: Through this paper and the pictures, the main results are showed as follows: 1. Membrane of bordered pit in earlywood tracheid is a typical Pinus structural type; 2. Bordered pits in sapwood are deposited by very little amorphous substances so that their fine structure is clear, most of them are aspirated, most tori are dished inward over the aperture; the bordered pit membranes in sapwood that is close to the boundary of heartwood become so thick that dish impressions are decrease. Bordered pits and pit membranes are deposited by the abundent matrix, encrustations and extraetives in the heartwood, so the completely incrusted membranes are formed and the passage between cells may be blocked. These may be the main factor of low permeability in larch wood; 3. This study reports that some thin or non-cellulosic film substances are deposited on the surface of pit borders, pit membrances and tracheid lumens, that may affect strongly the permeability of wood; 4. The ultrastructure of bordered pits in latewood is very different from that in earlywood sapwood. These bordered pits are small, the tori are thicker and bigger, the diameter of microfibrillar strands of margo in latewood (maxi. up to 3960(?), aver. 1839(?) and 2340(?)) is thicker and wider than that in earlywood (aver. 733(?)), these thick microfibrillar strands consist of several to many microfibrils and are covered by some amorphous substances, the shape of the bordered pit membrane openings in latewood is different from those in earlywood. These may cause the increase in the rigidity of pit membranes and the bordered pits to be unaspirated completely or aspirated partially; 5. The abundent matrix, encrustations and extractives are deposited or penetrated in the different layers of cell wall and around the microfibrils. These substances must block the fine structure and affect the nature of microcapillaries, that may be another main factor of the low permeability in larch wood; 6. This study indicates that the width or distance between microfibrils of the S₃ and S₁ layers is larger than that in S₂, the denseness of S₃ and S₁ is lower, the porosity is higher, especially the S₁ layer is clearer.