Abstract: BaTi_1-xAl_xO₃ (x=0.02, 0.04, 0.06, 0.08) were prepared by sol-gel methods. The crystal structure, microstructure and dielectric properties were investigated by X-ray diffraction method, scanning electron microscope and Agilent4284A testing analyzer respectively. The results reveal that BaTiO₃ is the main phase of the samples and the second phase BaAl₂O₄ is observed after Al³⁺ doping. With increasing Al³⁺ content, the average grain size decreased gradually; the density of samples increased from 5.46 g/cm³ to 5.81 g/cm³, but tended to stable as x≥0.06. What's more, dielectric constant decreased from 4766 to1834, temperature coefficient increased from 0.00132/℃ to 0.0018/℃ and the dielectric peaks broadened at 1MHz. Meanwhile, the stability of defect cluster 2Al_Ti′ +V_O^·· was -1.915 eV calculated by General Utility Lattice Program (GULP).