Illustration is always used as an example to make the written text or the utterance more clear in general. In Winarski’s opinion (1997), one picture equals thousands of words. That is to say, illustrations are capable to express the meaning of unfamiliar language or a great deal of information in the reading material by vivid pictures, tables, drawings, paintings and so on. As a result, illustrations are applied to many different fields including English language teaching. Based upon Song’s 3 types of illustration classification (2005), decorational illustrations, explainable illustrations and promotive illustrations, this paper tries to investigate the effects of illustrations on the reading performance of senior high school students with different cognitive styles (field-dependence, field-mix and field-independence) in the process of English reading. The result shows that: 1). There is a significant correlation between illustration types and reading performance in terms of field-dependent students. The coefficient of explainable illustration to reading peformance is the highest, while the lowest coefficient is decorational illustration. 2). As for field-mixed participants, their reading performance is also closely associated with illustrations. However, the coefficients are lower than that of field-dependent participants. Decorational illustration has no obviously relation to reading performance. Explainable illustration also reaches the highest coefficient, and it can better improve student’ reading score than promotive illustration. 3). Speaking of field-independent students, no correlation has been found between decorational, promotive illustration and reading performance. However, there exists a significant correlation between explainable illustration and reading performance for field-independent participants.