Crystal phase engineering on CuInS₂ (CIS) nanocrystals, especially polytypic structure, has become one of the research hotspots to design the advanced materials and devices for energy conversion and environment treatment. Here, the polytypic CIS nanosheets (NSs) including zincblende/wurtzite and chalcopyrite/wurtzite types were first time achieved in a hot-injection system using oleic acid and liquid paraffin as the reaction media. As-obtained polytypic CIS NSs exhibit significantly enhanced light-absorption ability and visible-light-driven photocatalytic performance originating from the rational hetero-crystalline interfaces and surface defect states, which efficiently inhibit the recombination of photo-generated carriers. Meanwhile, the polytypic CIS NSs were spin-coated onto the surface of fluorinated-tin oxide glass substrate and used as the photoelectrode, which shows an excellent photoelectrochemical (PEC) activity in aqueous solution. The present work not only provides a facile, rapid, low-cost, and environmental-friendly synthesis strategy to design the crystal phase and defect structure of ternary chalcogenides, but also demonstrates the relationships between the polytypic structure and photocatalytic/photoelectrochemical properties.