Abstract: Productive syntax constitutes a crucial component of children’s language development, yet relatively little is known about how Mandarin-speaking children with developmental language disorder (DLD) acquire syntax. This study employed a life-story narrative task to elicit longitudinal language samples from three pairs of age-matched DLD children and typically developing peers (TDA). An exploratory analysis of syntactic indicators revealed that DLD children exhibited significant deficits in overall productive syntax, as well as in three sub-dimensions—noun phrases (NPs), verb phrases (VPs), and sentence structures (SS). Moreover, the syntactic profiles of DLD children showed marked individual variability across specific constructions. By extending the Index of Productive Syntax (IPsyn) framework to preschool-aged Mandarin speakers and adopting a longitudinal design, this study not only documents persistent syntactic weaknesses in DLD but also highlights developmental heterogeneity and asynchrony. These findings provide novel evidence for understanding the linguistic underpinnings of DLD in Mandarin and contribute to refining clinical assessment and intervention practices.