Li _3xLa _(2/3)–x† _(1/3)–2xTiO ₃(LLTO) is a promising solid-state electrolyte for Li-ion batteries. We study the effect of Li content on the stability, electronic and Li-ion diffusion properties of LLTO surface based on first-principles and molecular dynamics simulations. We consider both Li-poor and Li-rich LLTO surfaces. The results show that La/O/Li-terminated LLTO (001) is the most stable crystal surface. Further, LLTO (001) surface gives better stability when Li content is 0.17, 0.29, and 0.38 for Li-poor phase, while 0.33, 0.40, and 0.45 for Li-rich phase . Electronic structure calculations infer that in both Li-poor and Li-rich LLTO(001) surfaces there occurs the transition from conductor to semiconductor with the increase of Li content. Besides, we find that Li-ion always keeps a two-dimensional diffusion path for different Li content. As Li content increases from 0.17 to 0.38 for Li-poor LLTO (001) surface, Li-ion diffusion coefficient increases gradually and Li-ion diffusion barrier decreases from 0.58 eV to 0.42 eV. Differently, when Li content increases from 0.33 to 0.45 for Li-rich LLTO(001) surface, it does not follow a monotonic trend for diffusion coefficient nor for diffusion barrier of Li-ion. In this case, Li-ion diffusion coefficient is the largest and Li-ion diffusion barrier is the lowest (0.30 eV) when Li content is 0.40. Thus, our study suggests that by varying Li content, the stability, band gap, and Li-ion diffusion performance of LLTO (001) can be changed favorably. These advantages can inhibit the formation of lithium dendrites on the LLTO (001) surface.