The present study made a reference to Zhu Dexi's phrase-based grammar approach to analyse Cantonese utterances hierarchically into 14 syntactic structures (SS). A total of 68 speech samples from Cantonese-speaking children with and without Autism Spectrum Disorder (ASD) were collected. The mean length of utterance in words (MLUw), the number of syntactic structures (NOSS), the number of different syntactic structures (NODSS) and the flexibility of syntactic structures (FSS) of the samples were calculated. Comparisons among four groups of typically developing (TD) children revealed that all the indexes show developmental changes across age stages. Comparisons between ASD subjects and their age-matched (AM) and MLUw-matched (MM) normal peers were done. MLUw, NOSS and NODSS and FSS could be used to distinguish autistic children from their AM normal peers, but only FSS could be used to distinguish ASD from MM groups qualitatively and quantitatively. The lack of production of SP, V1O/SV2 and Coord1Coord2 with low FSS may be one of the factors that will affect ASD children's further syntactic development.
Keywords: flexibility of syntactic structures; mean length of utterance in word (MLUw); syntactic structures; the number of different syntactic structures.