Abstract:A new method for the optimization of cut-off grade in open-pit was put forward, which was based on control theory. After a brief introduction to the analytical framework of calculus of variations with an overall equality constraint, a mathematical model for selecting an optimum cut-off grade function was constructed, which aimed at the maximization of total present value of an open-pit. Then a comparison was made, and it was shown that the new method yielded the same solution results as the traditional ones, and in some cases it avoided the iteration process which was needed by those traditional methods due to the mutural determination of cut-off grade and the maximum total present value of a mine. At last a calculation example was given.

Key words: cut-off grade　open-pit　control theory