Abstract: The final slope angle and mining depth are two key parameters that affect each other in the design of open-pit boundary，and their values are closely related to the safety and economy of open-pit mine.In order to discuss the reasonable values of the above two parameters，taking the 12# typical exploration line section of an open-pit copper mine in Tibet as the study example，based on empirical analogy method，the final slope angles of the western and eastern slopes of the section are preliminarily determined as 38°~44°，and the combination of different slope angles are selected.According to principal of the boundary stripping ratio less than economic stripping ratio，the calculated bottom elevation is from + 4 135 m to + 4 108 m.The finite element numerical model of the final slope of the open-pit boundary of the section is established.The safety factors of the western and eastern slopes are calculated by strength reduction method.According to the safety factors of the slope and the economy of mining，the reasonable final slope angle and mining depth of the section are obtained.The study results show that the stability of open-pit slope decreases gradually with the increase of final slope angle and mining depth，and the influence of final slope angle on the stability of slope is much greater than that of the opposite side slope，the two parameters influence each other and determine the safety and economic effect of open-pit mine together；the calculated reasonable final slope angles of the western and eastern slopes of the section are 42° and 43° respectively， with the bottom elevation is + 4 117 m and the total mining depth is 920 m.The above study ideal of synergistic optimization of final Slope angle and mining depth in open-pit mine can provide some reliable reference for the scientific determination of relevant parameters in open-pit mines.

Key words: Open-pit mining, Safety factor of slope, Final slope angle, Mining depth, Economic stripping ratio, Numerical simulation