Onomatopoeia plays a crucial role in the early language development of individuals, serving as one of the primary language symbols acquired at an early stage. It functions as a bridge, connecting external sounds with the language system. In this study, event-related potential technology was employed alongside a lexical decision task within sentence structures, introducing phonological and orthographic variables. The main objective was to explore the impact of sentence context on onomatopoeia processing among hearing-reduced (HR) students. The results showed that the accuracy of HR students was significantly lower than typical-hearing (TH) students. With sentence context, the P200 response to phonological similarity was significantly larger than the response to orthographic similarity in HR students, and the P200 response to orthographic similarity under sentence context conditions was smaller in HR students than in TH students. Compared to TH students, graphical similarity evoked a higher P200 in HR students. Moreover, the N400 in the contextless condition was lower than in the contextual condition in TH students. The findings revealed that sentence context can have an impact on the acquisition of meaning for onomatopoeic words, as well as the processing of their phonology and orthography, but the effect on HR students and TH students was different.