Abstract: In order to compare the reliability of resistance method and stress wave method and the detection effect of the two methods under different decay degrees of wood, 10 Fraxinus mandshurica trees with different decay degrees were detected by electrical resistance tomography system and stress wave tomography system. The tree decay degree（E_d） measured by the electrical resistance method and the tree decay degree（W_y） measured by the stress wave method were obtained. The control data-core mass loss rate（true decay degree of trees）（M_s） was obtained by processing and analyzing wood cores obtained by growth cones. The unitary linear regression equations between E_d and M_s, W_y and M_s were established respectively. Results showed that when the decay degree of living trees M_s＜30%, the results of resistance method were closer to the real value, and when the decay degree of living trees M_s≥30%, the results of stress wave method were closer to the real value.