This paper aims to investigate the effects of the alignment entailed in the continuation task on syntactic complexity in L2 written production. A total number of 48 sophomores majoring in English at a university in China were randomly assigned to two groups, one is the continuation group and the other is the topic writing group. The current study employs an advanced computational tool "the L2 Syntactic Complexity Analyser" to assess syntactic complexity in writing samples and focused on 7 indexes including three measures of length of production, two coordinate phrase measures, and two complex nominal measures. The result shows that significant differences exist in six of the syntactic complexity measures with the continuation group outperforming the topic writing group. It is demonstrated that the continuation task, which couples production with comprehension and entails the alignment effect, has a facilitating impact on improving the writing syntactic complexity for L2 learners. The implications of these findings for second language acquisition and L2 writing pedagogy are considered.