Micro segregation of Mg and Mn in a Al-Mg5.0-Mn0.5 aluminum alloy homogenized annealing at 470°C was evaluated by computational simulation in DICTRA? software, using MOB2 diffusion database and Al-based database. The segregation factor was used to predict the distribution of Mg and Mn at 470°C annealing temperature for different annealing time. Simulation results were compared with microstructure observations. After homogenizing at 470 oC for 8.3h, the segregation factor of Mg was about 0.94, close to 1.0; while, the segregation factor of Mn varied from 0.78 to 1.3. After homogenization annealing at 470 oC for 11.1h, the segregation factor of Mg was close to 1.0, and concentration of Mg was basically uniform, the range of segregation factor of Mn was almost unchanged. However, almost the same segregation factor of 0.8~1.3 was observed for Mn at the annealing temperature of 470 °C and annealing time of 27.8h. According to the DICTRA calculation results, after homogenizing at 470oC/11.1h, the micro-segregation of Mg was nearly eliminated. While the micro-segregation of Mn could not be eliminated, even if the annealing holding time extended to 27.8 h and 30h. This provides a reference for the selection of annealing process of Al-Mg5.0-Mn0.5 aluminum alloy.