Herein, BiOBr with (110)/(102) facet homojunction (BiOBr-2) was designed via crystal facet reconstruction in order to achieve the optimal interfacial charge separation rate, thus realizing the maximal photocatalytic CO2 conversion efficiency of the intrinsic photocatalyst. Without any co-catalysts and sacrificial reagents, BiOBr-2 exhibits 100% selectivity towards CO in pure water with an apparent quantum yield of up to 1.03% at 400 nm, much higher than 0.24% of BiOBr with a single (110) lateral facet. After light irradiation for 10 h, the CO yield of BiOBr-2 is 65.0 μmol g−1 h−1, 2.1 and 4.5 times higher than that of BiOBr with a single (110) or (102) lateral facet, respectively. DFT calculation further authenticates an unanticipated separation path bridged between (110) and (102) facets, which realizes dramatical in-situ spatial separation efficiency of electrons and holes in BiOBr-2. This study presents a novel approach to realizing superior charge separation and catalytic activity by optimizing intrinsic catalyst for artificial photosynthesis.