Sugi (Cryptomeria japonica D.Don) wood generally has the so-called black heartwood, which contains the extremely high moisture content. Although subjected to the drying process, it is difficult to be dried up com­pletely so that Sugi wood does not have the sufficient strength for use. The reason is that during drying pro­cess, the bordered pit membrane on traicheids closes faster near the heartwood in Sugi wood so that the internal moisture is not easily come out to the outside. At the mean time, it also makes very difficult to sa­turate the rotten-proof chemicals into the dried Sugi wood to have it become an additionally valuable wood. In this paper, we will develop an underwater shock wave technique to treat the pre-dried wood for the im­provement of the drying property as well as the permeability and strength of Sugi wood by selectively frac­turing the bordered pit membrane. The result indicates a very remarkable improvement on the drying time. The mechanism of the fracture of the bordered pit by underwater shock wave will be further studied in the future.