Modulating lattice strain in intermetallic compounds could effectively alter their electronic structure and binding energy, thus impacting catalytic activity. Strain is usually induced through lattice mismatch, achieved by constructing core-shell nanostructures or metal-substrate interfaces with complex reciprocity and distractors. However, in situ induced strain without interface-construction or lattice mismatch presents challenges. In this study, we precisely manipulate consecutive compressive strain from -0.5% to -0.8% in CoPt ₃Pd intermetallic compound by inducing interior atomic radius mismatch. Precise strain control results in a negative shift of d-band center, dynamic charge distribution, and facilitates water dissociation, leading to the enhanced electrocatalytic activity. The CoPt ₃Pd catalyst with -0.5% compressive strain exhibits exceptional hydrogen evolution activity, with an overpotential of 169 mV at 1 A cm ^-2. Our approach offers a straightforward method to manipulate compressive strain on intermetallic compound by atomic size mismatch, with broad implications for catalytic processes.