Both experiments and numerical simulations of the mixing and discharging processes of two-sized particles in a truck mixer were carried out. The discharged particles were divided into 10 groups of samples with same weight By comparing the big particle content (BPC) in discharged samples and the discharging time, the presented discrete element method (DEM) model was validated first Then, DEM simulations were further performed to investigate quantitatively the transition of axial segregation and the distribution of the BPC in the 10 discharged samples which is almost impossible by conventional physical experiments of state-of-art. In the numerical analysis of axial segregation transition, the mixed particles are also divided into 10 groups of samples with same weight according to their x positions. Numerical results reveal that the size difference of particles and the structure of the drum cause the occurrence and transition of axial segregation during the mixing process. Small particles readily fill in among the big particle clusters or the similarly size gap more easily, thus the small particles force the big particles out from the drum bottom, ultimately facilitating the axial segregation occurs and band of small particles is observed at the drum bottom (Sample 10) and widen to Sample 9 as mixing. The big particles being crowed out gradually move toward drum mouth causing the increase of BPC in other samples. During the mixing process, the relative movements are positively associated with the axial segregation: the stronger the relative moments are, the larger the speed and extent of the axial segregation are; the speed of total axial segregation decreases as mixing progresses, but the degree of axial segregation increases. The discharging process can somehow restrain and improve the axial segregation of the discharged samples. The falling back and feeding forward movements of the big particles make the BPC in discharged Samples 1 to 5 almost be consistent with the relevant mixed samples, whereas the BPC in discharged Samples 6 to 8 decreases and discharged Samples 9 and 10 increases. The transition of axial segregation during the mixing and discharging processes determines the BPC distribution in discharged samples following a parabola law. (C) 2016 Elsevier B.V. All rights reserved.