Abstract: Associative theory, constraints theory and social-pragmatic theory are three basic theories about how infants learn new words. We outline social-pragmatic evidence with respect to four questions：1) What kinds of social cognitive processes are involved in infants` word learning? 2) How does social-pragmatic theory refute the challenges from associative theory and constraints theory? 3) How is the weight of social cognitive process in infants` word-learning relative to associative learning or lexical constraint mechanism? 4) What difficulties do children with autism encounter in word-learning task via social cues? Current evidence strongly indicates that social cognitive processes play a basic role in infants` word-learning. Finally, some suggestions on future research are proposed.

Key words: word learning, infants, social-pragmatic, associative, constraints