This study aimed to develop an academic vocabulary list based on a textbook corpus. First, a corpus-based form analysis of elementary, middle, and high school textbooks was established. Second, a list of thought phrases was developed. Third, the selected academic vocabulary was graded. In this study, a balanced corpus (comprising 16,406,663 words) was constructed over four subjects: Korean language, humanities, social studies, and science from 361 elementary, middle, and high school textbooks in consideration of the unique characteristics of the textbook texts. From these, 1,387 monolingual academic vocabularies were selected using quantitative and qualitative methods. Additionally, by introducing a new methodology based on textbook characteristics and statistical principles, the academic vocabulary was classified into four grades.