Abstract: The quantification of depth for inner defects of heat exchange tubes in nuclear power plant was realized by acquisition data mapped under the linear fitting of phase against defect depth curve. But according to practical experience of data analysis, there still exists deviation in this method. In this paper, based on eddy current and metallographic anatomy data, new phase and amplitude calibration curves were fitted by nonlinear least squares method, and then the comparison of data accuracy as analyzed by statistic method between fitting curves and the original one was undertaken and it was shown that the new phase fitting curves were more accurate for data quantification.