Exciton–polariton coupling between transition metal dichalcogenide (TMD) monolayer and plasmonic nanostructures generates additional states that are rich in physics, gaining significant attention in recent years. In exciton–polariton coupling, the understanding of electronic-energy exchange in Rabi splitting is critical. The typical structures that have been adopted to study the coupling are “TMD monolayers embedded in a metallic-nanoparticle-on-mirror (NPoM) system.” However, the exciton orientations are not parallel to the induced dipole direction of the NPoM system, which leads to inefficient coupling. Our proposed one-dimensional plasmonic nanogrooves (NGs) can align the MoS2 monolayers’ exciton orientation and plasmon polaritons in parallel, which addresses the aforementioned issue. In addition, we clearly reveal the maximum surface potential (SP) change on intermediate coupled sample by the photo-excitation caused by the carrier rearrangement. As a result, a significant Rabi splitting (65 meV) at room temperature is demonstrated. Furthermore, we attribute the photoluminescence enhancement to the parallel exciton–polariton interactions.