Abstract: A kind of slab designing problem was brought forward, in which the weight of slabs is fixed and the customer order demand specifications of weight and width are interval values. A multi-objective model to minimize the number of slabs and the total surplus weight was built. Based on the idea of the order-slab matrix and the compatible set of slabs, a two-stage optimal algorithm was proposed to solve the problem. In the algorithm, the first stage is to minimize the number of slabs, and the second stage is to minimize the total surplus weight. For this algorithm, the optimal nature was proved theoretically and an application case was given based on practical data.