With　the　increasingly　urgent　safety　requirement　of　lithium-ion　batteries,　more　and　more　attention　has　been　paid　to　Li7La3Zr2O12　(LLZO)-based　solid　electrolytes　with　high　ion　conductivity　and　excellent　electrochemical　performance.　Unfortunately,　owing　to　the　serious　＂Li-loss＂　and　the　abnormal　grain　growth　(AGG)　during　the　long-time　high-temperature　sintering　process,　it　is　difficult　to　achieve　the　high-quality　LLZO　electrolyte　with　uniform　and　fine　grains,　high　density　and　excellent　electrochemical　performance.　In　this　work,　Ga/Mo　co-doped　LLZO　solid-state　electrolytes　have　been　prepared　by　traditional　sintering　(TS)　and　two-step　sintering　(TSS).　And　the　sintering　mechanism,　phase　stability,　microstructure　evolution,　and　electrochemical　performance　have　been　systematically　investigated.　A　small　amount　of　Ga/Mo　doping　not　only　promotes　the　formation　of　the　cubic　garnet　LLZO　phase,　but　also　enhances　the　stability　of　cubic　phase.　High　density　of　92.3%　and　uniform　microstructure　without　AGG　have　been　achieved　via　a　small　amount　of　Ga　doping　and　TSS.　Li6.3Ga0.1La3Zr1.8Mo0.2O12　electrolytes,　prepared　by　TSS　of　1200　degrees　C/15　min-1100　degrees　C/8　h,　exhibits　high　ion　conductivity　of　2.59　x　10-4　Scm-1　and　critical　current　density　(CCD)　value　of　0.5　mAcm-2,　low　electric　conductivities　of　4.77　x　10-9　Scm-1,　which　suggests　it　is　a　potential　electrolyte　to　apply　in　all-solid-state　batteries.