Piezoelectric materials are sensitive to lattice strain, which is always related with their macroscopic properties. Therefore, it is of scientific significance to improve piezocatalytic performance by strain engineering and clarify the underlying mechanism. Herein, BaTiO3 (BTO) powder is fabricated by a solid‐state reaction and ball‐milling is employed to induce lattice strain in BTO. By prolonging ball‐milling time, the lattice strain increases, leading to an enhancement of tetragonality and piezocatalytic performance of BTO. The strain‐engineered BTO exhibited an excellent piezocatalytic activity, with a degradation rate constant k of ∼0.03 min−1 and a H2 evolution rate of 0.899 mmol g−1 h−1, which are 3 and 3.52 times those of the strain‐free one, respectively. The enhanced piezocatalytic performance can be ascribed to the improved piezoelectricity, piezoelectric polarization and adsorption activities for O2, OH and H of the strain‐engineered BTO. This work not only provides a simple and general method to improve piezocatalytic performance by strain engineering, but also unveils the enhancement mechanism.