Although the wider electrochemical window, higher temperature stability, and better battery safety of Li7La3Zr2O12 (LLZO) electrolytes than organic liquid, organogels, and polyelectrolytes, the limited ionic conductivity still far away from the practical electrochemical applications. Herein, LLZO electrolytes were by solid phase method. In order to further improve its electrochemical performance, aluminum doping was introduced to replace Li+ sites and thus the highly conductive cubic phase was stabilized. The results show that with the increase of the doping amount, the ion conductivity presents a trend of first increasing and then decreasing. It was found that 0.15Al-LLZO ceramics presented optimized ionic conductivity (1.184×10-4 S·cm-1) and 92.5% of bulk density at 1150 ℃ for 21 h treatment. On the other hand, with the combination of molecular simulations, the relationship between the influence of aluminum doping on the differential charge density of the garnet solid electrolyte and the electrochemical performance was investigated. It is believed that such an experimental-modeling combination will expand the fundamental understanding of elements variation/doping effects on solid electrolytes, especially for lithium metal oxides.