The study investigated the development of lexical diversity and syntactic complexity, two key indicators of writing quality, in Chinese second language (L2) writing. The Guiraud Index and T-unit length were used to measure lexical and syntactic growth through a cross-sectional design. Seven hundred and sixty-five narrative essays were collected from grade 3-6 students in Singapore's primary schools. Statistical analyses showed a general upward trend in lexical and syntactic development over the 4 years. In line with a dynamic account, the lexical and syntactic components grew in a non-linear and non-parallel manner with both progress and regress during the process. Furthermore, a trade-off was found between more varied word use and longer sentences in the data, though it faded with grade level. While L2 subsystems tended to compete with each other at earlier stages of language learning, their interactions changed over time. Moreover, variations were observed not only across grade levels but also between learner groups at the same stage of learning. By extending a dynamic approach to writing development at early stages of Chinese learning, the study informs theory regarding the dynamics of L2 growth and has significant implications for the teaching of Chinese writing in the Singapore context.