<p>This study used Event-Related Potential (ERP) technology to investigate the neural mechanisms underlying orthographic-phonological automatic integration in Chinese adults with Reading Fluency Difficulty (RFD). Twenty-two fluent Chinese readers (mean age = 22.41, 9 males) and 19 individuals with RFD (mean age = 21.37, 5 males) participated in this study. The Mismatch Negativity (MMN) component, elicited through a cross-channel passive oddball paradigm, served as a neural index to examine orthographic-phonological automatic integration. The study found that adults with RFD in Chinese exhibited significantly smaller MMN compared to normal readers in both the A (auditory) and AV_0 (simultaneous audiovisual) conditions. Additionally, individuals with RFD displayed significantly larger MMN in the AV_100 condition compared to the A condition, and they exhibited a tendency for right-hemisphere engagement in orthographic-phonological automatic integration during the AV_100 condition. These findings indicate that adults with RFD experience deficits in orthographic-phonological automatic integration, necessitating a wider temporal window to achieve integration levels comparable to fluent readers. The involvement of the right hemisphere in this process may indicate a compensatory mechanism due to functional abnormalities in the left hemisphere. However, the deficits in orthographic-phonological automatic integration may be associated with impairments in phonological automatic processing and working memory limitations, suggesting that the factor of orthographic-phonological automatic integration may not function as an independent contributor to RFD.</p>