Business textbooks play an important role in business knowledge learning, so the translation of business textbooks is very significant. A distinctive feature of business textbooks is the abundance of illustrations. This study takes the translation of illustration texts in business textbooks as a representative to explore the translation techniques of business textbooks. Previous studies have shown that free translation is usually used to translate illustrations, which is mainly achieved by addition and deletion. Although these studies have listed the content that should be added and deleted, they have not clearly stated why addition and deletion are used when translating illustrated texts. Therefore, they do not have a unified standard to guide the translation techniques of business textbooks, and they are unable to clearly indicate how to use addition and deletion and what are the reasons for addition and deletion when translating business textbooks. Based on the boundary awareness theory, this paper discusses the English-Chinese translation techniques of illustrations in Understanding Business and its two Chinese versions(10th edition and 12th edition). There are two basic English-Chinese differences in the boundary awareness theory: 1. Chinese and Chinese speakers’ boundary awareness is weaker than English and English speakers; 2. English and English speakers are more prospective and have a stronger prospective awareness, while Chinese and Chinese speakers are more retrospective and have a stronger retrospective awareness. According to this theory, we can find that the translation techniques of addition and deletion are: adding the translation of words with resultant meanings, such as nouns, verbs, and adjectives, and deleting the translation of words that have the function of dividing sentence structure, such as prepositions, relational adverbs, and relational pronouns. The reason for using both translation techniques is to weaken the strong boundaries of the English language to match the weak boundaries characteristic of the Chinese language.