The invention discloses an A-site and B-site co-doping strontium titanate mixed conductor material with A-site deficiency. The material is a product in which A-site of perovskite type SrTiO3 is doped with 30 mol% of La and B-site of perovskite type SrTiO3 is doped with 4 mol% of Sm, and a molecular formula after co-doping is (La0.3Sr0.7)1-xTi0.96Sm0.04O3-delta, in which x is equal to 0.05 to 0.09. A preparation method comprises the following steps: using a compound containing lanthanum, samarium, strontium and titanium to configure raw materials according to a stoichiometric proportion of the (La0.3Sr0.7)1-xTi0.96Sm0.04O3-delta; compounding the configured raw materials into A-site and B-site co-doping SrTiO3 powder in an air atmosphere at the temperature of 900 to 1200 DEG C with a sol-gel method; grinding the powder into fine powder with 100 to 200 meshes; adding 10% to 50% of an inflammable substance into the fine powder for press molding, and calcining for 2 to 12 hours at the temperature of 1300 to 1600 DEG C so as to obtain a mixed conductor block body. According to the material, on the basis of La doping, un-equivalent metal ions are doped on the B-site of the material, so that the ion deficiency concentration is improved, and the ionic conductivity and comprehensive conductivity of La-doped SrTiO3 are improved.