In recent years, with the increasing difficulty of the National College Entrance Examination English test, reading comprehension and writing have become the main sections where students lose scores. As a critical linguistic resource for comprehending authors’ intentions and expressing one’s own attitudes and viewpoints, metadiscourse exerts a potential effect on improving students’ reading and writing proficiency. This study adopts artificial intelligence (AI) as an auxiliary tool for metadiscourse instruction: teachers generate teaching materials with the support of AI, while students use AI to identify metadiscourse markers and obtain writing feedback. The aim of this research is to explore an effective approach to promoting English reading and writing proficiency by strengthening students’ metadiscourse awareness. The research was conducted with two parallel classes as research subjects. The experimental class received AI-assisted instruction during metadiscourse teaching, while the control class adopted conventional teaching methods. The teaching effect was tested by comparing pre-test and post-test scores of reading and writing, and analyzing the frequency of metadiscourse use in students’ compositions. The results indicate that the post-test reading scores and total writing scores of the experimental class are significantly higher than those of the control class, and the frequency of metadiscourse use, such as transitions and frame makers, in the compositions of the experimental class increased remarkably. Additionally, there is a significant positive correlation between the frequency of metadiscourse use and total writing scores. The research findings demonstrate that AI-assisted metadiscourse instruction can effectively improve the English reading and writing proficiency of high school students. Based on these conclusions, this paper puts forward teaching suggestions from the dimensions of metadiscourse identification training, integrated reading and writing instruction, and AI-assisted feedback mechanisms, so as to provide references for English reading and writing teaching in high schools.