Barium strontium titanate is a promising material for microwave-phased array applications. In this study, highly dense and fine-grained Ba0.6Sr0.4TiO3 ceramics were prepared using the spark plasma sintering (SPS) technique. The structure and dielectric tunable properties of the samples were investigated. The "distorted nano-region" emerged in the interior of the grains of SPS samples, and resulted in the deterioration of the dielectric tunable properties of BaxSr1-xTiO3. This phenomenon indirectly testified to the assumption of the "polar nano-region" mechanism. After the SPS samples were annealed, the ''distorted nano-region" disappeared and better dielectric tunable properties were obtained. The dielectric constant was decreased to 1048, and the K value (Commutation Quality Factor) reached 7089.