The invention provides an alkali metal ion-electron mixed conductor, a preparation method thereof and a solid-state battery. The conductor has ionic conductivity and electronic conductivity at the same time, and comprises three components: a polyvinyl acetal single-ion conductor polymer, electronic conductive polymer poly (3, 4-dioxoethylthiophene)/poly (p-styrenesulfonic acid) and organic alkalimetal salt. The conductor provided by the invention is a polymer flexible body, wherein the tensile strength is greater than or equal to 40 MPa, the plastic deformation is greater than or equal to 150%, the Young's modulus is greater than or equal to 5 GPa, the electrochemical window is greater than or equal to 4.8 V, and meanwhile, the room temperature ionic conductivity is larger than 10<-4> S/cm and the electronic conductivity is greater than 10 S/cm. The alkali metal ion-electron provided by the invention is applied to a solid-state battery comprising an alkali metal ion battery and an alkali metal battery, and is beneficial to improving the proportion of an active material in the solid-state battery and the energy density and cycle life of the solid-state battery.