1、 Introduction

In recent years, the number of German language learners in China has significantly increased, but there is a lack of relevant research. Written language proficiency is a hot topic in language acquisition research, and syntactic complexity is a key indicator for measuring the written language output of foreign language learners. The research under the dependency grammar framework provides a new perspective on syntactic complexity. This study is based on the theory of dependency grammar, quantitatively examining the development trend of written syntactic complexity among Chinese high school German learners, and explaining its development pattern from a qualitative perspective. The study aims to answer two questions: 1) the impact of increased learning duration on the syntactic complexity of written German; 2) The reason for this trend.

2、 Theoretical basis and literature review

Deeply explored the concept of syntactic complexity and its application in assessing written language proficiency. Syntactic complexity typically refers to the diversity and complexity of grammatical structures, involving the length of language production units and the density of use of specific grammatical structures. Researchers have proposed various measures of syntactic complexity based on different theories, including sentence length, subordinate structure, and parallel structure. Liu (2008) proposed the average dependency distance as a new indicator for predicting the difficulty level of text syntactic structure, emphasizing the role of working memory in language production.

3、 Research Design

This chapter elaborates on the research design in detail, including three parts: corpus source, dependency annotation and proofreading, and data analysis. Firstly, 180 essays were selected from the corpus of Chinese German language learners, divided into five levels with 36 people in each group. The essay genre was narrative, with themes related to daily life. Secondly, use spaCy software to automatically annotate the dependency relationship of the composition, and use EXCEL and TIGER annotation libraries for proofreading to solve annotation errors. Finally, Microsoft Excel and SPSS software were used to quantitatively analyze the dependency annotation results, calculate the average dependency distance, and conduct one-way ANOVA to explore the development of learners' written sentence complexity. At the same time, by observing the corpus through qualitative methods and mining the language production characteristics at different stages, the quantitative analysis results can be verified.

4、 Results and Analysis

By analyzing the development of written sentence complexity among Chinese German learners, this study reveals the changing trend of dependency distance in students' compositions at different stages of learning. Research has found that the average dependency distance of students significantly increases from Stufe1 to Stufe3, indicating an increase in syntactic complexity. However, from Stufe3 to Stufe5, this growth trend slows down and the increase in syntactic complexity is not significant. The distribution analysis of absolute dependency distance (ADD) shows that as the learning stage progresses, the proportion of adjacent dependency relationships (ADD=1) decreases, while the proportion of larger dependency distances (ADD ≥ 6) increases, which is consistent with the trend of the average dependency distance. Through specific example sentence analysis, it was found that learners in higher grades are able to use more complex and diverse syntactic structures, such as multi-level clauses, although these structures are not commonly found in the corpus. The stagnation of syntactic complexity growth may be related to teaching input. In junior high school, students are exposed to various syntactic structures through systematic learning, while in high school, there is a lack of further systematic learning and practice, leading to the development of syntactic complexity entering a plateau period.

5、 Summary

We constructed a dependency tree library for German language from grade one to grade two and explored the development path of syntactic complexity in high school students' German language. Research has found that syntactic complexity significantly increases in the first three years, with no significant changes in the later stages. This is consistent with Li's (2022) research findings, indicating a stagnation in syntactic complexity in the later stages of learning. The reason may be related to the teaching input, as learners are greatly influenced by the classroom and textbooks. The lack of systematic syntactic learning and sufficient training in the higher grades leads to a lack of significant development in syntactic complexity in the later stages. Teachers and students should be patient and not overly anxious. In high school, students should continue to systematically learn syntax and be encouraged to consciously use complex sentence structures. Future research can track the language development and changes of the same group over a period of three to five years, and explore in depth the reasons for the non-linear development of language in the middle and high stages.