Aiming at loss and depletion of mineral resources caused by poor effect of selection and mining in the process of open pit mining, we research the influence of mining process, mining procedure and bench height on the effect of selection and mining through theoretical analysis and calculation. The selection and mining effect of different equipment is analyzed to select the optimal mining technology according to the characteristics of different types of coal and rock. Taking the mining model with a single bench as the research object, we analyze and calculate the selection and mining indexes of different advancing directions, and establish an optimization model of minimum thickness of coal seam with the goal of maximizing the economic benefits. By establishing mathematical model, the relationship between step height and coal loss rate, rock mixing ratio, minimum recoverable thickness and minimum thickness is deduced, and then the method to improve the effect of selection and mining by optimizing the bench height is found out. Baiyinhua No.2 open-pit mine is taken as an example and the results show that by choosing proper mining technology, advancing method and optimizing the height of the bench height, the selection and mining effect of the open pit mine can be effectively improved.