Textbook analysis is vital for the improvement of college English teaching, and a python-based method is proposed for the analysis of such textbooks. This method is based on a pre-constructed database of short, medium and long words (determined by n-gram frequency analysis of the Google’s Trillion Word Corpus). It is generally held that the selection of reading materials should transition gradually from easy to difficult, from simple to complex, reflecting a development process from shallow to deep. Considering this fact, the research question of this paper is to test the lexical complexity of a textbook and try to find out whether the four books of the textbook transition gradually from easy to difficult in terms of lexical complexity. It is found that the four textbooks contain roughly the same rate of short, medium and long words, thus supporting the fact that the four textbooks are appropriate for college English teaching and at the same time the feasibility of the method is approved. Another two methods are used to support the result.