The invention provides a novel quasi garnet-structured lithium ion conductor (Li7-xLa3Zr2-xSbxO12, wherein x is more than 0 and less than or equal to 0.5) crystalline-state ceramic solid electrolyte material and a synthesis method thereof, and belongs to the field of lithium ion batteries. A novel quasi garnet-structured lithium ion conductor is synthesized by conventional solid-phase reaction. X-ray diffraction (XRD) diffraction peaks of Sb-doped samples show that the Sb-doped samples all have crystalline -state cubic phase quasi garnet-structures in the Sb doped range. The maximum lithium ion conductivity can reach 3.42*10<-4>S/cm at room temperature (30 DEG C). The sample is synthesized by the conventional solid phase method, a preparation process is simple, and sintering time is short. Zr is partially replaced by high-valence Sb, so the lithium ion vacancy is increased, the ionic conductivity is improved obviously, and antimonous oxide is low in price compared with zirconia, so manufacturing cost is reduced. Therefore, the synthesized compact ceramic solid electrolyte material can be probably applied to a lithium ion battery.