The low photocatalytic conversion efficiency, poor light absorption and high charge recombination rate of traditional semiconductor photocatalysts continues to be a significant research challenge. In this paper, by combining detailed experimental and modelling techniques, we report on the unique potential of CaBi₂Nb₂O₉ (CBN) platelets that can couple both piezo- and photo- multi-field effects to overcome these issues and realize high-efficiency hydrogen production and dye degradation. The surface adsorption of OH⁻ and dye molecules is improved as a result of the built-in electric field, thereby demonstrating an enhanced piezo- and photo-catalytic H₂ production activity, with a high rate of 96.83 μmol•g⁻¹•h⁻¹. The piezo-photocatalytic decomposition ratio for 100 mL RhB dye of 10 mg/L can reach up to 98.7% in 32 min using only 0.05 mg of CBN platelets (k = 0.131 min⁻¹). It is shown that the careful introduction of regularly arranged layers of (Bi₂O₂)²⁺ into the CBN platelet structure provides a high transport of photoelectrons via a pathway of (Bi₂O₂)²⁺ → (CaNb₂O₇)²⁻ → CBN surface. The electron density distribution of Bi atoms is also found to be enriched on the facets of (020) and (200) crystal planes in the CBN platelets, which is beneficial to the oxidation reduction reaction. Furthermore, the large deformation of CBN platelet during the application of ultrasound leads to an increase of the piezo-induced built-in electric field to improve charge separation and migration. This work therefore provides a new perspective in the design and manufacture of advanced materials with enhanced piezo- and photo-catalytic performance by exploiting multi-field coupling effects.