Advancement in virtual reality (VR) technology has enabled language learners to be engaged in immersive and interactive learning environments. Recent studies have revealed that the educational use of VR technology can improve students' writing achievement, behavioral engagement, and cognitive engagement in learning. However, the factors contributing to these improvements are not fully understood. Writing programs that foster a positive writing self-concept is helpful for students' development. In this study, adopting the self-determination theory as the theoretical lens, the affordances of VR contributing to students' self-concept in descriptive writing (DW) were explored through a newly adapted survey. Secondary school students (n = 300) who attended a VR-supported writing course completed the survey that measured their responses to five related factors: (1) autonomous observation; (2) relatedness; (3) self-efficacy; (4) satisfaction; and (5) writing self-concept. Exploratory and confirmatory factor analyses were conducted to validate the five-factor survey measurements. The results indicated that the construct validity and reliability of the survey were acceptable. A structural equation model was constructed to investigate the hypothesized relationships of the factors contributing to the students' writing self-concept. The results indicated self-efficacy and satisfaction directly predict students' writing self-concept, and relatedness indirectly predicts writing self-concept. These findings reveal the underlying mechanism which could inform educators who are keen on promoting or harnessing VR-supported learning and teaching in writing education.