<p>Writing is a core component of literacy and an important foundation for later academic development. However, research on the development of underlying writing dimensions and their associations with writing content quality remains limited, particularly in the Chinese context. This study examined grade-related differences in four dimensions of writing skills—character, vocabulary, grammar, and discourse—and their associations with writing content quality among 188 Chinese primary school children in Grades 1, 3, and 5, using an open-ended narrative writing task. The results showed that writing content quality, number of characters, token count, type count, vocabulary diversity, and discourse cohesion increased across grades. Character accuracy, punctuation accuracy, and syntactic complexity improved from Grade 1 to Grade 3, whereas vocabulary accuracy and grammatical accuracy did not differ significantly across grades. Partial correlations controlling for grade and sex showed that writing content quality was positively correlated with most writing-skill indicators, with vocabulary diversity showing the strongest correlation. In the full-sample mixed-effects model, vocabulary diversity showed the strongest unique association with writing content quality, and grammatical accuracy also showed an independent association. Grade-specific analyses further suggested that the relative importance of writing-skill indicators may differ across grade levels.</p>