The band structures, lattice parameters, densities of states and bond characteristics of two different Li₇La₃Zr₂O₁₂ (LLZO) solid electrolyte materials in tetragonal and cubic phases were calculated by the first-principles method based on density functional theory (DFT). The reason why the ionic conductivity of the tetrahedral phase is lower than that of cubic phase was explained by the electronic structural characteristics based on the theoretical calculation results. Two kinds of crystalline structure LLZO materials were designed based on first principles calculation of LLZO and prepared by the high temperature solid phase method, and the properties of LLZO pellets with different sintering time were analysed. The effect of the synthesis process parameters on the properties of Li₇La₃Zr₂O₁₂ was explored. Results show that the average lattice size of cubic Li₇La₃Zr₂O₁₂ (C-LLZO) is a=b=c= 1.302 246 nm, while that of tetragonal Li₇La₃Zr₂O₁₂ (T-LLZO) is a=b=1.313 064 nm, c=1.266 024 nm. The C-LLZO sintered at 1000 ℃ for 12 h has a pure cubic phase and a maximum ionic conductivity of 9.8×10^-5 S·cm^-1 is realized at room temperature (25 ℃). The ionic conductivity of T-LLZO at room temperature (25 ℃) is 5.96×10^-8 S·cm^-1, which has a pure tetragonal phase structure after sintering at 800 ℃ for 6 h, basically in agreement with the calculation results.