The aim of this study was to uncover how sufficiently senior high school English textbooks in Taiwan prepare students for reading the passages in the high-stakes college entrance examinations in terms of text difficulty. A corpus-based approach was adopted to compare the vocabulary load and readability of passages extracted from senior high school textbooks and from the English test papers of college entrance examinations. Two corpora were compiled: a textbook corpus comprising texts extracted from all five editions of Ministry of Education (MOE)-authorized senior high school textbooks and a test corpus containing all of the reading passages in the college entrance English tests from the 2002 to 2017 school years. The results indicate that the passages in the English textbooks do not match those in the tests in terms of the vocabulary load and several Coh-Metrix readability metrics. The reading passages in the English tests generally have lower overall readability, lower narrativity, and higher syntactic complexity than those in the textbooks. The test passages also require a much larger vocabulary size than the textbooks do. Implications of the findings for students, textbook writers, English teachers, and the MOE are provided.