Anxiety is widely recognized as a significant affective factor that influences second language (L2) writing proficiency. However, its specific contributions to writing motivation and engagement, and how it interrelates with these constructs, are not clearly defined. To address this research void, this study explored the role of anxiety in the relationship between motivation and engagement in Chinese as second language (CSL) writing among 229 Vietnamese university students. A variety of specialized Chinese writing tasks were designed for this study, and quantitative research methods were utilized. The findings revealed that motivation in writing indirectly influenced behavioral engagement through anxiety, showing a positive correlation with both constructs. Contrary to expectations, anxiety did not impede learners' performance. Additionally, the study uncovered that the students' consistent attitudes toward Chinese writing and their self-awareness protected their cognitive engagement from potential disturbances of affective anxiety. Furthermore, the research indicated a significant impact of anxiety across various segments of the Vietnamese student population, while the moderating effect of "different writing tasks" was negligible. The study also suggested that task selection, aligned with Vietnamese university students' preferred learning styles, could potentially increase their interest in the Chinese language without reducing their motivation and engagement in writing tasks.