Teachers should help students learn subject matter knowledge through their pedagogical content knowledge. The use of metaphors in instructional materials may be one of the ways to help students to learn subject matter knowledge. This study explored whether students who used instructional materials with metaphors (experimental group) could acquire better subject matter knowledge than other students (control group).The results revealed that metaphorical design only slightly improved students' test scores, but students preferred the instructional materials with metaphorical design. Therefore, appropriate use of metaphors in the difficult parts of instructional materials is still valuable and necessary. This study also proposed several suggests for teaching practice research in future.