Abstract: Lumber microwave treatment results in structure changes of treated, it will enhance liquid permeability of treated lumber to make it easier for functional processing. In order to uncover the mechanism of permeability increase during microwave treatment, six species of wood were treated by high intensity microwave in present study.Microstructure changes such as the separation of the ray parenchyma with axial tissue, unfolding of the aspirated pit , broken up in the wood cell wall, the distribution change of the tyloses in pores were found in Scanning Electron Microscopy (SEM) pictures taken before and after microwave treatment. These microstructure changes resulted in the mechanical properties decrease, in which the MOE decreased by 31.1%、35.4%、45.6%、5.5%、24.4% and 23.2% respectively for Chinese Fir(Cunninghamia lanceolata (Lamb. ) Hook. ), Siberian Larch(Larix gmelini (Rupr. ) Rupr. ), Mongolian Scotch Pine(Pinus Sylvestris L. var. ),Chinese White Poplar(Populus tomentosa Carr. ), South China Paulownia (Paulownia australis Gong Tong), (E. urophylla E. grandis), while MOR decreased by 38.4%、29.4%、67.2%、9.1%、34.0% and 29.1%. Besides, different kinds of microstructure changes existed in different wood can also result in different water absorption rate changes for treated lumbers.According to the tests results, the species which are suitable for functional processing can be determined.