Abstract: The calculated depth of defect by software is not accurate when the defect is not in the middle of two probes, which due to the existence of the error of axis deviation in the process of TOFD inspection. However the distance between the defect and the middle of two probes cannot be measured by the TOFD software. The signal of transformed wave was made use of, then the time difference among the diffracted longitudinal wave signals of cracks and transformed waves signals was surveyed, and the calculated depth was modified by iterative procedure. Finally the distance of the defect deviating from the middle of two probes was drawn out. The feasibility of this method was verified by the theoretical derivation and experiment. Then the detailed information of eccentricity and accurate depth of defect could be got by using TOFD image.