To examine the relationship between hearing impairment and cognitive function and the mediating role of social isolation and depression. Methods: Data came from the 2018 China Health and Retirement Longitudinal Study wave. A self-reported item, a composite index, the 10-item Center for Epidemiological Studies Depression Scale, and the Mini-Mental State Exam were used to measure hearing impairment, social isolation, depression, and cognitive function, respectively. Mediation analysis was performed. Results: 6799 participants were included. For participants reporting mild hearing impairment and severe hearing impairment, there were significant direct and indirect effects on cognitive function. Social isolation mediated 2.75% and 6.33% of the relationship between mild hearing impairment, severe hearing impairment, and cognitive function, respectively. The direct effect of hearing impairment outweighed the mediation effect of social isolation on cognitive function. Conclusions: Decreased cognitive function linked to hearing impairment might benefit from addressing hearing impairment and social isolation in older adults.