Steel balls of different sizes may have uneven axial distribution in the rotating drum, which will cause different crushing effects in different areas of the ball mill. As a result, the working efficiency of ball mills cannot be accurately reflected by traditional evaluation indicators which assume that the balls are uniformly distributed along the axis. The existence of axial segregation of the steel balls was verified by including balls of different sizes in the drum through the experiment and simulation (Discrete element method) model. Different size balls in the drum tend to separate from each other while the same kind of balls gather along the axis. The segregation of different types of balls causes uneven distribution of collision and energy in the ball mill. Based on the basic assumption that the crushing energy is related to the energy loss in ball collisions, the concept of regional total energy (or RTE, for short) is put forward to evaluate the axial inconsistent crushing effect in different areas caused by axial segregation in the drum. The regional total energy in the ball mill under axial segregation is sampled and calculated by the Monte Carlo method. The calculation results show that the distribution of the broken energy in the region is related to the distribution of the ball, and the region with more balls has greater crushing energy, which also means better crushing effect. Thus, it is necessary to study the crushing effect of ball mills with the consideration of regional total energy. (C) 2019 Elsevier B.V. All rights reserved.