With the reform of the new college entrance examination, senior high school English writing has received great attention. The English Curriculum Standards for Senior High Schools (2017 Edition Revised in 2020) proposes that English teaching in senior high schools should focus on cultivating students’ core competence in the English discipline. In particular, English writing, which can fully reflect students’ comprehensive English application skills, plays a significant role in English learning. However, according to current learning situation, the writing performance among senior high school students is not satisfactory. In the recent years, the importance of functional adequacy as an essential component of L2 proficiency has been observed by some scholars. Based on this, this study highlights the effectiveness of functional adequacy in facilitating students’ writing performance and emphasizes the importance of developing students’ pragmatic writing ability. Also, this study explores how to develop functional adequacy in senior high school students’ writing and puts forward some pedagogical implications of improving pragmatic performance in writing for English teachers.