1、People have been paying more and more attention to the interfaces between second language acquisition (SLA) and language testing (LT), and they have found that the orientation of interfaces between SLA and LT on tasks ha

2、s already been proven appropriate. Various researches on task-based language teaching and testing have been conducted over the past dozen years and many inspiring findings and various models about the task-based oral and

3、 written language have been obtained. Based on the model put forward by Robinson (2001), this paper intends to investigate the influence of task difficulty and task complexity on the students' performances on the wri

4、ting tasks.Results show that task difficulty and task complexity have great influence on the students' writing,that is, with the increase of the difficulty/complexity levels, students' performances on the tasks decrease

5、accordingly, and the students' perception of task difficulty/complexity has close relationship with their performances on the writing tasks, but the students' specific performance variables in the tasks do not change a

6、ccordingly with the difficulty/complexity levels. The present study shows that we can design the courses and carry out task-based teaching and testing and effectively develop the students' writing abilities by manipula