This paper explores the function and influence of L1 transfer in second language acquisition, with a specific focus on English learning within the Chinese context. Language transfer acts as a dual force in the learning process; while inter-lingual commonalities rooted in universal grammar can facilitate positive transfer and boost learner confidence, the structural and conceptual differences between languages often trigger negative transfer, leading to language errors and learning difficulties. Focusing on English writing instruction, this study demonstrates that the tracks of L1 negative transfer are highly conspicuous across vocabulary, grammar, and cultural thinking dimensions. Specifically, students frequently misapply word forms due to differences in plural concepts, omit necessary subjects because of the distinct subject-predicate relations in Chinese, and produce rigid “Chinglish” expressions by directly applying native thinking habits to English sentence building. To address these issues, the paper suggests that teachers should provide targeted guidance—such as analyzing typical mistakes, contrasting sentence patterns, and cultivating target-language thinking—to effectively minimize the negative interference of the mother tongue and progressively improve students’ comprehensive writing literacy.