The effect of cone-in-cone insert on the flow pattern of ABS plastic balls in a hopper during their discharging process was studied and simulated with discrete element method. Firstly, the micro parameters of ABS balls were measured and verified by physical experiments. Then the relationship between the structural parameters and the flow pattern was studied via orthogonal experiments, and the distribution of compressive force on the hopper wall analyzed. The results show that the angle of cone-in-cone insert has the most important effect on the flow pattern, the second one is the distance between the cone-in-cone insert and discharge outlet, and the third is the height of the insert. The funnel flow can not change into mass flow when the angle of cone-in-cone insert is smaller than 120o. With the appropriate cone-in-cone insert fixed in the hopper, the maximum compressive force on the hopper wall is reduced to the half of its original value, and its location moves up.