Task-Based Language Teaching proposes the notion of task as a central unit of planning and teaching. There is now a considerable volume of literature on task (Prabhu， 1987； Nunan， 1989； Wills， 1996； Eills， 2003). In addition， task has increasingly been used as a unit for research into second language acquisition (Crookes &Gass， 1993). Therefore， task has become an important tool for the language teacher and a basic unit for language research. The concept of task itself is not a new one. In second language pedagogy， different scholars have put forward different interpretations from different aspects. As Willis (1996： 32) emphasizes that the target language should be used for the communicative goal to show their achievement of language learning in a task. Nunan (1989： 8) also indicates that learner should interact with others in the target language ......