Abstract: In industrial production,it is often necessary to remove the surface decarburization layer to prevent the work piece cracking during subsequent processing due to uneven hardness and structure. Therefore, the prediction of decarburization layer depth is of great significance. The decarburization behavior of 42CrMo steel was discussed at different holding temperatures,the differences in the morphology of decarburization layer was observed by metallographic microscope. Then the decarburization layer depths were statistically compared. Based on Fick′s second law and analyzing the decarburization kinetics behavior of 42CrMo steel at holding temperatures ranging from 1 023 to 1 373 K, a theoretical calculation model was established for decarburization layer depth of 42CrMo steel. At the same time, through the metal high-temperature oxidation theory combined with the oxidation weight gain experiment, the oxidation and loss behavior of 42CrMo steel at different holding temperatures was discussed, and the model was revised. Through metallographic analysis and microhardness distribution analysis, it was proved that the theoretical value of decarburization layer depth obtained from the corrected decarburization layer depth calculation model was basically consistent with metallographic test value, verifying the accuracy of the model. This indicated that the decarburization layer depth calculation model designed in this work could effectively predict the decarburization layer depth.