Heterostructure construction has been regarded as a feasible pathway for nanomaterial fabrication towards optimized properties. Despite impressive investigations on heterostructure fabrication, assembling distinct polymorphs to form heterojunction has seldom been focused on relevant aspects. In this work, we demonstrated tunable localized surface plasmon resonance (LSPR) by Cu2S/CuS polymorphs via cation-triggered self-assembling on SnS2 substrates. During the transformation, the forming of covellite phase proceeds through cation exchange, while the simultaneous formation of chalcocite phase was achieved by the variation of the redox states of the anion framework. Furthermore, the formed polymorphs with optimized proportion on SnS2 substrates exhibited enhanced charge-carrier-involved processes by intrinsic band alignment in distinct polymorphs, resulting in excellent photocatalytic performances compared with those single-phase dominant copper sulfides on substrates. We thus hope this controllable nanostructure fabrication with distinctive properties could provide some useful hints for photo-electrochemistry applications.