Template growth and catalytic growth are two typical mechanisms for the solution-chemistry synthesis of one-dimensional (1D) II–VI semiconductor nanomaterials. Here, we systematically demonstrate the competition relationship between them by tuning the synthesis of 1D ZnS nanostructures in different chain-length primary alkyl-amines. The template growth, derived from the coordination effect of amines, produces ZnS nanobelts and will compete with the Ag₂S-catalyzed mechanism as AgNO₃ is added into these amines. In short-chain n-propylamine and n-butylamine the template growth is much stronger than the catalytic growth, leading to the morphology maintenance of ZnS nanobelts, whereas the latter replaces the former in long-chain n-octylamine and n-dodecylamine due to the decrease of coordination ability of amines, which yields ZnS nanowires instead of nanobelts. A balance of competition is built between these two mechanisms in middle-length n-hexylamine, producing a mixture of ZnS nanobelts and nanowires. The morphology and growth mechanism changes of ZnS nanostructures have been rationally investigated using various characterization techniques. Meanwhile, the optical properties of the products synthesized before and after adding AgNO₃ are comparatively studied by UV-vis absorption and photoluminescence (PL) spectra.