We herein demonstrate the uniform porous hierarchical plate-like BiOCl/2D networks Bi2S3 heterostructures realized by a facile two-step hydrothermal technique. The synthesis involved an anion exchange process by reacting pre-synthesized BiOCl irregular octagonal nanoplates with Na2S2O3 center dot 5H(2)O in an aqueous solution. The experiment results revealed that the 3D plate-like heterostructures were composed of internal BiOCl and outside networks interwoven by 1D Bi2S3 nanorods. Interestingly, the heterostructures had almost the same thickness and the bigger length compared to the precursor BiOCl. We proposed the possible formation mechanism of the composites which involved selective ion-exchange reaction, the following Ostwald ripening process and epitaxial growth. And the crystal lattice matching between the a- or b-axis of tetragonal BiOCl (a = b = 3.89 angstrom) and the a-axis of orthorhombic Bi2S3 (a = 3.981 angstrom) could be responsible for the in-situ topotactic transformation. Due to the formation of hetero-nanostructures, the unique spatial architecture features and the existence of oxygen vacancies, the BiOCI/Bi2S3 composites exhibited significantly extended photo-responsive range and improved photocatalytic activity for reduction of Cr-VI under visible-light irradiation. Moreover, the possible mechanism of photocatalysis process was investigated. Our work is expected to inspire further attempts for hierarchical and unconventional hetero-nanostructures with unique spatial architecture, which is very promising for photo catalysis and other applications.