Abstract: Scanning white light interferometer and scanning electron microscope were used to observe the surface wear states of hot forging die of automobile flange and reveal its wear failure mechanism. In addition, based on the abrasive wear model developed by Archard, the thermo-mechanical coupled FE model of the hot forging process was built to estimate the influence of initial die temperatures, forging rate and heat treatment method on the wear depth of die. The results demonstrate that three types of wear mechanism were observed on the worn surface, namely adhesive wear, oxidation wear and abrasive wear. Abrasive wear was the most serious, which caused a maximum wear depth about 100μm. According to the numerical results, when the initial temperature of die was 250℃ and the forging rate was 300 mm/s, the maximum die temperature after forging was lower than the allowable temperature of AISI H13(about 620℃), and it rendered the minimum wear depth of die after forging. Also, compared with the quenching and tempering method, by using plasma nitriding, the maximum wear depth of die dropped from 7.2×10^-5 mm to 1.3×10^-5 mm. The wear depth of die was reduced by 82% and the service life of die was improved by 5.5 times. The experimental result had a good agreement with the predicted one.