Solid-state electrolyte is the core component of all-solid-state lithium battery with the characteristics of high safety and high energy density. The typical representative Li7La3Zr2O12 (LLZO) has been paid extensive attention by researchers due to its high ionic conductivity, high mechanical strength, high electrochemical stability, low interfacial impedance, and good stability for lithium metal anodes. However, compared to liquid-state electrolytes, problems such as lower ionic conductivity and less contact with the solid-solid interface of electrodes in LLZO still exist. This research mainly introduced effects of the crystal structure and modification method of LLZO on its performances of ionic conductivity and interface impedance. Existing problems of LLZO were summarized, and future development directions were prospected. This research provides theoretical guidance for the practical production and application of all-solid-state lithium batteries.