This study aimed to compare and analyze the relationships and performance characteristics of imitation, social interaction, and emotional expression in children with autism spectrum disorder (ASD), global developmental delay (GDD), and typical development (TD). A total of 105 children aged 2-6 years (35 ASD, 35 GDD, 35 TD) were assessed using the PEP-3 to evaluate imitation abilities (physical imitation and social-emotional imitation), social interaction, and emotional expression. Descriptive statistics, exploratory factor analysis, correlation analysis, and analysis of variance were conducted. Exploratory factor analysis of the imitation domain yielded two factors: “physical imitation” and “social-emotional imitation.” Group comparisons showed that children with ASD exhibited the lowest performance in both physical and social-emotional imitation, children with GDD showed intermediate performance, and TD children showed the highest performance. Social interaction and emotional expression also differed significantly among the three groups, and a high positive correlation between social interaction and emotional expression was found in children with ASD and GDD. These findings suggest that the developmental profiles of children with ASD and GDD differ both qualitatively and quantitatively, and that imitation may serve as an important evaluative index for early diagnosis and the design of function-based individualized interventions.