Research on the effects of the socioeconomic status (SES) on literacy development of children with intellectual disabilities (ID) is limited. This study aimed to explore the SES's influence on literacy development of children with ID and possible mediating effects of home literacy environment (HLE) and the parent-child relationship. The subjects of this study were 390 children with ID from special needs schools in 14 regions of China, including 239 boys and 151 girls aged 7 to 15 years. This study adopted the network survey method, with parents of children with ID completing surveys on SES, HLE, literacy development, and the parent-child relationship. SES was found to positively predict literacy development of children with ID. Further, it was found that HLE played a mediating role in the prediction of literacy development by SES, and the parent-child relationship regulated the positive impact of HLE on literacy development. In conclusion, SES significantly influences literacy development of children with ID which is partially mediated by HLE. The parent-child relationship positively regulates the regression relationship between HLE and literacy development.