Abstract: Cut-off grade is an especially important decision-making parameter for mines.As grade indicators were developed in the planned economy era in China，current mining industry index cannot adapt to the development with the improvement of China′s market economy.Shaxi Copper Mine is a deep-buried，large-reserve and low grade mine.One of the great issues on how to make exploitation economic is the cut-off grade.In view of this，the mineralized domains with a copper grade of 0.1% are delineated for the boundary，then.geo-statistics are made to get the mineralized domain models to achieve average grade and grade of the ore reserves.The cutoff grade dynamic optimization mathematical model and algorithm are proposed by maximizing the net present value.Finally，the method above optimized the cut-off grade of Shaxi Copper Mine.Comparing with the results for the preliminary design，the mine life，recycled metal，total cash flow，total net present value have been significantly improved by this method.It also provides a reference for exploitation of large-reserve，low grade underground deposits in China.

Key words: Cut-off grade, Dynamic optimization, Mineralized domain modeling