Investigating catalytic behavior of heterogeneous catalysts, especially at the crystal facets level, is crucial for rational catalyst design in the energy and environmental fields. Here we demonstrate an efficient approach to in situ visualize and analyze the heterogeneity of electrocatalytic activity on different facets at the subparticle level via electrochemiluminescence (ECL) microscopy. ZnO crystals with various exposed facet proportions were synthesized, and the correlation between their electrocatalytic performance toward luminol analogue degradation and the exposed facets is established. It is clearly imaged that the ZnO (002) facet has superior catalytic performance compared to the ZnO (100) facet, which is supported by theoretical computation and electrochemical experiments as the facet-induced heterogeneity of the catalytic effect on oxygen reduction into the key reactant for ECL. Accordingly, the spatial heterogeneity of electrocatalytic activity at different facets on one particle is visualized for the first time. The realization of subparticle ECL imaging and kinetic analysis could provide a special approach to visualize facet-induced spatial heterogeneity of catalytic behavior and valuable information for the catalysis study and analysis.