The present research set out to investigate the effect of working memory on English reading comprehension of Chinese middle school students. To do so, we recruited 150 Chinese students at grade 8 and conducted two studies. Study 1 examined the predictive power of working memory on the performance of English reading comprehension, grammar, and writing. Results showed that working memory has a significant positive correlation with English grammar or writing and that working memory is the key predictor of English reading comprehension of Chinese middle school students. Recruiting 80 students out of those 150 participants in Study 1 based on their performance of English reading comprehension, Study 2 further explored the effects of different components of working memory on English reading comprehension. Results showed that verbal working memory and the updating function respectively exert great influence on English reading comprehension of Chinese middle school students. The findings can help L2 teachers understand the importance of working memory in reading comprehension and encourage them to design learning and teaching materials that match with students' working memory capacity.