The Discrete Element Method (DEM) is used to simulate the mixing and discharging processes of binary particles in a laboratory truck mixer. The contact parameters in the DEM model are calibrated by experiments and then used to simulate the particle mixing and discharging processes in truck mixer under seven groups of operation parameters. Numerical results show good agreements with the experimental data in terms of the big particle content (BPC) of discharged samples and the discharging time (T-d). It is found that the discharging speed of 8 rev/min produces the largest discharging rate (D-r) whereas the discharging homogeneity is the lowest. The highest discharging homogeneity is observed when the discharging speed is 5 rev/min. The effects of filling rate and mixing speed on the discharging rate are insignificant. The mixing homogeneity decreases with the increase of mixing time, mixing speed and filling rate, which result in the discharging homogeneity also decreasing with the increase of mixing speed and filling rate.