Barium strontium titanate (BarSr1-rTiO3, BST) ferroelectric material is considered an important material in dynamic random access memory, microwave tuner, phase shifter, and other applications because of its good dielectric, ferroelectric, and pyroelectric properties. In this study, the (1-r)Ba0.6Sr0.4TiO3-rSnO2 (BST-Sn) ceramics were prepared via the solid-phase sintering method. The effects of different contents of SnO2 on the microstructure and dielectric properties of the BST system were examined via X-ray diffraction, scanning electron microscopy, and the LCR digital bridge test system. The theoretical calculation results show that the ratio of lattice constant c to lattice constant a of BST decreases and the band gap increases with an increase in the incorporation ratio of SnO2. When the doping ratio of SnO2 is 0.05, the band gap reaches a maximum of 1.889 eV. The results of band and state density show that an increase in band gap is caused by the movement of Ti atoms’ 3d orbitals towards high energy. Secondly, the dielectric constant of pure BST ceramics, prepared experimentally, is 3 227, and the introduction of SnO2 reduces the dielectric constant of BST ceramics.