Topological nodal-line semimetals have emerged as a fascinating class of materials due to their protected band crossings and unique electronic properties. Among them, ZrSiS stands out as a typical system with nodal-line and high carrier mobility. Although its bulk properties have been extensively studied, the optical and plasmonic behaviors of its monolayer and bilayer ZrSiS are still unexplored. Understanding these low-dimensional forms is crucial for harnessing their potential in nanophotonics and optoelectronic devices. This work, based on first-principles calculations, systematically investigates the electronic band structure, optoelectronic conductivity, optical response, and surface plasmon polariton (SPP) characteristics of monolayer and bilayer ZrSiS. The results are compared with those of bulk materials and typical two-dimensional materials, argentene, to explore their advantages and disadvantages in all aspects and application prospects. Our results show that layered ZrSiS exhibits distinctive conductivity features arising from its topological nodal-line bands, displaying a significant intraband response in the infrared regime and interband response in the visible range. Analysis of the optical properties reveals that both monolayer and bilayer structures possess high absorption (significantly higher than that of graphene) and tunable reflection and transmission windows in the infrared-to-visible spectrum range. Furthermore, regarding plasmonic properties, we find that monolayer ZrSiS and bilayer ZrSiS support SPPs in the infrared-to-visible range (monolayer: 0.5–4 eV; bilayer: 0.4–2.5 eV). These SPPs are highly localized, with confinement ratios several times larger than those of bulk ZrSiS, while maintaining propagation lengths on the order of micrometers in the infrared regime. In summary, monolayer and bilayer ZrSiS combine tunable electronic structure, high optical absorption, and strongly confined surface plasmons, making them promising candidates for advanced nanophotonic and infrared optoelectronic applications. Their layer-dependent properties provide additional degrees of freedom for device design, paving the way for next-generation tunable plasmonic and photonic devices.