Abstract: A nondestructive testing method based on the effect of magnetic Barkhausen noises (MBN) is proposed to detect the carburized depth of gears which are milled. Firstly, a carburized layer of 3 mm thickness is got by carburizing treatment. Then, the samples owning different carburized depths are milled with same feed rate (0.1 mm). Finally, the Barkhausen noise detection platform was used to test the samples with different carburized depth. The results show that the relationships between the root-mean-square (RMS) value and the mean value of Barkhausen noise signal and the carburized depth are linear. It is shown that the depth of carburized layer can be tested by the root-mean-square value and the mean value of Barkhausen noise signals.