Abstract: The distinction between short-term working memory and long-term working memory is that the former is capacity-limited while the latter is available to expert s in their domain of expertise. Text comprehension is viewed as expert performan ce, which is the process of psychological representation to the reading contents according to the text and one's own background knowledge, therefore, this paper analyzes the role of long-term working memory in text comprehension with an em phasis on the activation of relevant knowledge in the process and thinks that th e latent semantic analysis (LSA) is used to model knowledge activation through t he relation between words, paragraphs and words and paragraphs.