This study explored the concurrent and longitudinal relationships between reading and writing in young Chinese-as-a-second-language (CSL) learners' sentence writing, using structural equation modeling. The participants comprised 126 Hong Kong senior primary ethnic minority students, whose literacy skills were assessed at two time points over the course of a year. In grade 5 (Time-1), they were assessed with Chinese character reading and reading comprehension measures to evaluate their reading ability. In grade 6 (Time-2), their sentence reading, sentence writing, and literacy component skills of Chinese character writing fluency and written syntactic skills were assessed. The results demonstrated that students' reading and writing performances were substantially related both concurrently and longitudinally. Furthermore, (1) at Time-2, the component skills accounted for substantial portions of variance in sentence reading and writing skills, along with the relationship between them, while (2) Time-1 reading ability predicted Time-2 component skills and, through the mediation thereof, indirectly predicted sentence writing. Thus, in light of the linguistic characteristics of the Chinese language, literacy component skills are crucial component processes that connect reading and writing in CSL learners' sentence writing.