Four wood rot fungi were used to decay 300 mature trees of white birch in Liangshui experiment stations,and the mass loss of the samples was measured to study bio-degradability of the wood by the fungi. The decaying susceptible and resistant populations in 10 trees each with the highest and lowest mass loss were selected,in which some main chemical components in decayed and non-decayed wood such as lignin and cellulose and so on was tested. The result showed that the decomposing power of Coriolus versicolor to wood samples was better,and then were Fomes fomentarius,Irpex lacteus and Pholiota adiposa were poor. 1%NaOH extraction in decayed wood was significant higher than that in non-decayed control. Benzene-alcohol extraction in the wood decayed by Coriolus versicolor and Fomes fomentarius was significant higher than that in non-decayed control,but much lower than the control in the wood decayed by Irpex lacteus. The lignin decomposing rate by Irpex lacteus,Pholiota adipose and Fomes fomentarius were faster than the cellulose decomposing rate,the contrary result was achieved by Coriolus versicolor. This paper would provide some useful information in future study in the course and mechanism of wood decaying by rot fungi,and select engineering fungi for paper-making industry and pollution control.