The rapid advancement of AI-assisted automated writing evaluation (AWE) systems has brought significant changes to English education, particularly in English-as-a-foreign-language (EFL) learners’ self-regulated learning (SRL). This transformation is partly attributed to the potential of AWE to enhance learners’ writing self-efficacy and subsequently improve their writing performance. However, the impact of AWE on Chinese university students’ writing self-efficacy in English SRL remains unclear. Therefore, this study aims to investigate: (1) the current application features of the AWE system Grammarly among Chinese university students, (2) the correlation between the frequency of Grammarly usage and their writing self-efficacy, (3) the relationship between the purpose of Grammarly usage and writing self-efficacy, and (4) the correlation between the function choice of Grammarly and writing self-efficacy. A total of 336 valid questionnaires were collected from Chinese university students, and quantitative data analysis was conducted using SPSS 25.0 and AMOS 24.0 software. Results indicate that most participants are familiar with and satisfied with Grammarly, primarily using it to correct grammar and improve writing accuracy. Moreover, application fluency is positively correlated with writing self-efficacy, and the chosen functions of Grammarly yield different correlations. These findings not only provide insights for educators to effectively integrate English AWE systems into SRL but also offer guidelines for technologists to further develop relevant technology.