Herein, the heterogeneity of the facets potentials is used to improve the SERS activity of anatase TiO₂ single crystals co-exposed with {0 0 1} and {1 0 1} facets. Using methylene blue (MB) as the model molecule, the influence of the exposed-facet-ratio on the SERS activity was explored. The molecules prefer to be adsorbed by defective {0 0 1} facets, but the SERS activity is not proportional to the enlarged {0 0 1} facets. The single crystal exposed with 20% {0 0 1} facets (S₀₀₁20%) shows the highest SERS activity and a high EF of 8×10⁵ can be achieved. Based on the experimental analysis and density functional theory calculation, the SERS activity is proportionally correlated with the mobility of photo-induced electrons on defective {0 0 1} facets, which is promoted by the surface electric field pointing from exposed {1 0 1} facets to junction edge, and then to {0 0 1} facets as a result of heterogeneous facets potentials.