Mining classification rule of spare parts is very important for inventory management. In traditional classification work of spare parts, the attributes of spare parts were used as a standard to extract classification rules, but it was hard to know the influence of every attribute of spare parts, and which one should be considered, because the attributes of spare parts had many species. So it was necessary for inventory management to mine classification rules of spare parts. Because the values of many attributes of the spare parts are in form of the range of data, the grey rough set theory was borrowed to mine the classification rules in this paper. Firstly, the mining classification rules model of spare parts was built by the grey rough set theory. Then the attributes of spare parts were summarized, and the steps of mining data samples and the mining classification rules of spare parts were introduced respectively. Finally, case study from the classification management of the spare parts of a maintenance factory shows that the proposed mining classification rules model of spare parts based on grey rough set theory can reduce the unnecessary attributes of spare parts without affecting the results of classification.