This study presents a contrastive analysis on compositions by Chinese English majors across four grades and those of native speakers. It investigates the characteristics of written language in Chinese English majors in terms of lexical complexity and syntactic complexity, exploring the mutual relationship between the two complexities. Lexical complexity is measured by lexical diversity and lexical sophistication, while syntactic complexity is assessed through T-unit length, T-unit complexity ratio, and complex nominals per clause. One-way multivariate analysis of variance (MANOVA) reveals that the measures of lexical and syntactic complexity improve gradually from grade 1 to grade 4. Compared with native speakers, Chinese English majors demonstrate significantly lower measures, except for lexical diversity and the T-unit complexity ratio, which are similar to those of native speakers. The measures of lexical and syntactic complexity are largely independent of each other, with few significant correlations observed. This study provides important insights for further research on second language writing instruction in practice.