Heteronanostructures have attracted intensive attention due to their electronic coupling effects between distinct components. Despite tremendous advances of nanostructure fabrication, combining independent polymorphs by forming heterojunction is still challenging but fascinating, such as copper sulfides (Cu2-xS), exhibiting varying band gaps and crystal structures with various stoichiometries. Herein, self-coupled Cu2-xS polymorphs (Cu1.94S-CuS) by a facile one-pot chemical transformation route have been reported for the first time. Unprecedentedly, a manganous precursor plays a crucial role in inducing and directing the formation of such a dumbbell-like architecture, which combines 1D Cu1.94S with 2D CuS. During the transformation, Mn2+ ions mediate the Cu+ ions diffusion and phase conversion process particularly. Furthermore, this self-coupled polymorphic structure exhibits significantly enhanced photoelectrochemical properties compared with the individual Cu1.94S nanocrystals and CuS nanoplates, originating from the unique heterointerfaces constructed by intrinsic band alignment and the enhanced contact between high conductivity hexagonal planes and the working electrode revealed by density functional theory (DFT) calculations. So we anticipate this emerging interfacial charge separation could provide useful hints for applications in optoelectronic devices or photocatalysis.