An adequate discharging homogeneity of fresh concrete is the benefit of avoiding segregation and pipe blocking. In this article, the discrete element method was used to simulate the discharging process of fresh concrete in truck mixer. GB/T 9142 was used to examine the discharging homogeneity through five samples. It was found that the content of coarse aggregate is higher in the first and fifth samples but lower in the third sample than the standard C30 fresh concrete. The homogeneity of the second and fourth samples is higher than the others. These findings are consistent with experimental observations. Moreover, the standard deviation was proposed to scale the discharging homogeneity of mixture, which could present more comprehensive information besides the five samples used in GB/T 9142 standard. The effect of mixing speed, mixing time, discharging speed, and oblique angle on the discharging homogeneity was further discussed. The numerical results reveal that the discharging homogeneity of fresh concrete increases when the mixing speed increases from 1 to 2.5 rev/min, but decreases when the mixing speed further increases from 2.5 to 3 rev/min. The discharging homogeneity increases with the decrease of discharging speed, the oblique angle, and the transport mixing time.