In middle school English teaching, grammar instruction has always been an important and challenging aspect. Due to the strong influence of grammar explanation in Chinese, learning English grammar may be affected by negative transfer from their native language, which could pose certain obstacles to English acquisition. Self-efficacy, as a major emotional factor influencing learners' internal regulation strategies, has attracted wide attention from researchers both domestically and internationally for its impact on learning performance. High self-efficacy helps learners develop a more positive mindset towards learning, thereby contributing to improved learning performance. Therefore, this study focuses on investigating the relationship between grammatical self-efficacy and learning performance of English grammar among middle school students. This research contributes to a complementary understanding of grammatical self-efficacy among educators, enhancing their teaching skills, and effectively guiding students to learn English grammar with a more positive and healthy mindset, presenting a future grammar instruction in middle school English teaching.