Abstract: The ion-nitriding surface modification of 15Cr14Co12Mo4Ni2 material was carried out. The microstructure and property characteristics of the modification layer in three different heat treatment states were researched after15Cr14Co12Mo4Ni2 ion nitriding at 500 ℃ for 35 h, 60 h, and 120 h. The results show that through XRD analysis, the in-situ precipitation of Fe₄N and a small amount of Cr N crystalline nitrides in the nitriding surface layer are found. With the increase of ion-nitriding time, the diffraction peaks of Fe₄N are sharpened, and its content increases continuously, resulting in a thickening of the effective nitriding layer. Through SEM analysis, the presence of a “dark zone” in the ion nitriding layer is found, Cr and Mo in the strong nitride phase are enriched as “bright narrow stripes”, while N appears as “wide bands”. Both the quantity of Cr and Mo elements entering the lattice points and the content of high modulus nitrides precipitated in-situ during ion nitriding determine the magnitude of the microhardness of the nitriding layer on the surface. The relationship between the depth of the ion-nitriding layer and time in solution-treated samples follows Fick’s diffusion law. After complete heat treatment, the effective layer thickness of sample being nitriding for 120 h is 0.27 mm. The large numbers of nitrides are in-situ precipitated and the modification layer is strengthened after nitriding at 500 ℃, when Cr and Mo elements are completely solid soluted in the lattice dot matrix. Under solid solution treatment +primary ice cold and complete heat treatment, the contents of Cr and Mo elements in the lattice matrix decrease, and the number of nitrides in situ precipitated decreases. At a distance of 0.05 mm from the modification surface, the microhardness highest for the sample in the sate of solid solution heat treatment and the lowest in the state of complete heat treatment.