In view of the problems existed in delineating the open-pit boundary by traditional manual work such as low accuracy and heavy workload, a new method is presented on the basis of Economic Block Value Model (EBVM) with applying Lerchs-Grossmann algorithm to solve boundary optimization problems in large and complex open-pit mine, in order to improve the design efficiency and economic benefits. Not only a means of structuring EBVM is elaborated, but also a mathematical model of linear programming is constructed to solving optimization problems. Moreover, steps of Lerchs-Grossmann algorithm are described from the point of view of the set theory. The method has been realized in DIMINE software, and applied to the actual boundary optimization and design of open-pit mines. Results show that the method is able to overcome the shortcomings of traditional manual methods and solve the optimal exploitation scenarios quickly and accurately under different parameters. It provides basis and assurance for mining company with the optimal use of resources.