21世纪初，任务型教学法被广泛应用到中学英语教学中，而任务的难度是影响中学生表现的许多因素之一，但有关任务难度对学习者的影响多数是关于口语。本研究以Skehan (1996) 的衡量任务表现的三个尺度和Robinson (2001) 提出的关于任务难度和复杂度的理论为基础，以普通高中高三的40名学生作为研究对象来研究任务的难度对写作的影响。研究对象每人完成三项不同难度的写作任务并完成随后的调查，学生的写作从流利度、准确度和复杂度三方面来评价，并随后收集有关学生对任务难度认识和评价他们的写作表现的数据，同时收集学生对任务的难度的认知和他们写作水平之间的关系的数据。利用所收集的数据, 分析任务难度对高中学生写作的影响并得出以下结论：在某种程度上，任务难度影响高中学生写作的流利度、准确度以及句子的复杂度。如果任务难度低，学生写作的流利度和准确度就高。如果任务难度高，学生会使用较多的复杂句子来表达自己的想法，但是由于中学生的词汇量有限，任务的难度对词汇的复杂度影响不明显。此外，中学生对任务难度的认知和他们的写作表现有一定相关性，难度和兴趣与学生写作表现中的准确度和词汇的复杂度关联明显。本研究希望能够有利于对中学阶段任务型教学大纲的设计和任务型教学中任务的设计。同时也希望能够帮助中学阶段的教师更好的进行写作教学。在写作教学中，教师应选择难度适中的写作任务，同时考虑学生对任务难度认识的影响。文章最后指出了研究的不足和进一步的研究方向。

Since task-based language teaching (TBLT) was introduced into China at the beginning of the 21st century, tasks have been widely used in the English language classrooms in middle schools. Many factors influence students’ performance, among which is task difficulty. There is a lot of research investigating the influence of task difficulty on learners’ performance, but most of them are about oral aspect. The present study is based on Skehan (1996)’s framework and Robinson (2001)’s model of task complexity and task difficulty to investigate the influence of task difficulty on senior high students’ writing performance. Forty senior high school students participated in the research and finished three writing tasks of different difficulty levels. Their writing performance was measured in terms of accuracy, fluency and complexity. Data about the students’ perception of task difficulty were also collected through a questionnaire. Based on the collected data, the influence of task difficulty on the students’ performance is analyzed and the results are as follows: To some degree, task difficulty has an influence on the students’ performance as for fluency, accuracy and complexity in terms of syntactic complexity. If the task is easier, they are likely to produce more correct clauses and verbs. If the task is more complex, they are likely to produce their writings with higher syntactic complexity. However, because of the students’ limited vocabulary, task difficulty has no significant influence on their writing performance in terms of lexical complexity. Also, the students’ perception of task difficulty corresponds with their actual performance in three writing tasks. Difficulty and interest in particular have an influence on senior high students’ writing performance.The results of the study are of help to syllabus designers, designing tasks and teachers’ teaching writing in senior high school. In teaching writing, teachers should choose writing tasks with proper difficulty. Meanwhile the influence of the students’ perception of writing tasks should also be taken into consideration. Suggestions for further research are put forward.