Being immediate, rapid and effective,internetbased instant message(IM) is being used more and more.It is seen that there is a tendency to replace the fixed telephone and email by VoIP,with its development. According to Technology Acceptance Model(TAM)，the reason why internet users have intention to accept instant message service in China were explored from five aspects, perceived usefulness，perceived ease of use，flow experience，perceived playfulness and privacy. The effects of these factors on the intention to using instant message were studied by structural equation model(SEM). Some suggestions and future research directions are also put forward.