Abstract: During the transition from open pit to underground mining, a reasonable scale of production is necessary and feasible by optimizing it through the application of fuzzy mathematics. By applying the fuzzy comprehensive evaluation theory and taking all factors into consideration, this paper selects the five comprehensive evaluation index including the total investment, operation cost, net present value, length of service, increased employment, builds a fuzzy and comprehensive evaluation model of production scale of mines, and then uses it to optimize the scale of production during the transition from open pit to underground mining.