In this work, a unique Cu2O hexapod microcrystal with {100} facets etched concave structure has been successfully synthesized by a facile oxide etching method. Air and chloride ion were employed as etchant and shape controller agent, respectively. For the facet-selective adsorption of chloride ions on {110} and {111} planes, the oxide molecules may prefer to act on {100} facets and induced the concave structure formation, along the [100] zone axis. The {100} facets selectively etched Cu2O concave hexapod microcrystal exhibited highly improved photocatalytic activities (2.2 times) than that of basic structure, and displayed facet-dependent characteristics, which made them promising candidates for photocatalysts and sensing materials.