The pursuit of high-performance piezo-photocatalysts through structural modifications has been a focal point of investigation within the realm of related scientific disciplines. In this study, we successfully designed Er-doped Bi0.5Na0.5TiO3–BaTiO3 combined with rare earth ion doping and solid solution modification, and the prepared particles exhibited homogeneous grain sizes and optimized concentrations of oxygen vacancies (OV). The synergistic incorporation of OV (accelerator for catalytic reaction) and Er3+ results in an impressive 12-fold enhancement of the piezo-photocatalytic rate when degrading the Rhodamine B dye. The optimal composition 0.96BNT-0.04BT-Er demonstrates outstanding electrochemical properties, including a superior photocurrent response and minimal impedance, highlighting its exceptional performance in piezo-photocatalysis. The fundamental enhancement in catalytic performance can be attributed to the reconfiguration of the band structure of 0.96BNT-0.04BT-Er, which has been meticulously calculated utilizing DRS and VB-XPS and the internal mechanism was explained in detail. This research serves as a source of inspiration for the investigation of solid solutions among piezo-photocatalysts and sheds light on the vital role of band structure in governing catalytic performance.