Emotion comprehension refers to the ability to understand one's own emotions and predict the emotional state of others in different situations. Although there is substantial evidence showing the interconnective relations between language ability and emotion comprehension in preschool children, it remains unclear what psychological mechanisms underlie their bidirectional modulatory effects and how working memory and temperament type of children might alter their mutual influence. This study addressed this issue using a sample of 158 preschool children-mother pairs. Children completed an emotion comprehension test, a working memory task, and a language test task, and mothers reported their children's temperament type. Results showed a significantly negative association between emotion comprehension and language ability, in which preschoolers with higher emotion comprehension exhibited lower language ability. Working memory partial mediated this relation, and children's temperament types moderated it. These results suggest that processing emotional information is not only important for social adaptation but also for linguistic growth, emphasizing the importance of considering cognitive capacity essential for language development and temperament differences when examining language development in preschool children. These findings also provide a new perspective for understanding the relation between emotion and language for preschool children, and also provide a theoretical guidance for preschool educators and parents to promote children's language development.