本文对二语学习者英语写作表现中的语法复杂度的测量及测量效度进行了实证性研究。为检验测量指标的效度，我们以“中国学习者英语语料库”中的大学英语六级考试作文为样本，检验了T单位、从属小句、非限定动词和衔接成分在测量英语学习者书面语语法复杂度方面的效度。研究表明，上述四个指标能较为有效地反映出测量样本的语法复杂度，其中，T单位、非限定动词和衔接成分对书面语语法复杂度的发展具备预测功能。研究还发现，非限定动词指标在统计检验中优于其他三个指标，而从属小句在测量学习者书面语语法复杂度的发展方面的结果不如其他几项显著。

This paper theoretically and empirically addresses the issue of measuring the grammatical complexity of English language learners’ writings. For testing the validity of certain measuring indices, the authors gauged the sample articles’ T-units, dependent clauses, non-finite verbs and connectors based on Chinese Learners’ English Corpus and found that these indices are valid in measuring second language learners’ writing grammatical complexity. Meanwhile, T-units, non-finite verbs and connectors may well predict the development of the grammatical complexity of the second language learners. The study also discovered that non-finite verb is a trustworthy index in measuring second language learners’ grammatical complexity in writing for its better performance in the statistical tests of this study. The results indicate that the non-finite verb is a special index in measuring learners’ language complexity while dependent clauses contribute less significantly to the development of learners’ grammatical complexity.