Abstract: The relationship between the cut-off grade and the ultimate pit was analyzed under the conditions of technological and economical parameters change. Based on production data of Sijiaying open pit mine， the model of break-even grade was established to calculate the cut-off grade for needn’t to be mined and the cut-off grade for must be mined under the different conditions of market. According to the value of cut-off grade， the ultimate pit was optimized in different market context. For a preset cut-off grade， the ultimate pit was optimized at the same market context， and the ultimate pits of two methods were compared. The results indicated that under the same condition of market， the ultimate pit based on break-even method is better than that based on the preset cut-off grade.

Key words: open pit mine, ultimate pit, break-even method, cut-off grade, cone exclusive method