The purpose of this study was to investigate the effects of representation sequences and spatial ability on students' scientific understandings about the mechanism of breathing in human beings. 130 seventh graders were assigned to two groups with different sequential combinations of static and dynamic representations: SD group (i.e., viewing static representations and then dynamic ones), and DS group (i.e., viewing dynamic representations and then static ones). Among them, 16 students (8 from each group) with different levels of prior knowledge and spatial ability were interviewed. Data sources included a spatial ability test, pre- and post-tests of scientific understandings (involving factual, conceptual, and spatial knowledge), and semi-structured interviews. The statistical results indicated that the SD sequence helped students gain significantly more factual knowledge. The significant interaction effects further suggested that while the representation sequences had no effect on students with low spatial ability, high spatial ability students in the SD group outperformed than their counterparts in DS group on the items of the conceptual and spatial knowledge. Additionally, the analysis of interviews indicated that the representation sequences could affect the foci of students' explanations and shape their perceptions about the representations. The results suggested interplays among representation sequences, spatial ability, and students' understandings, and provided insight into the design and arrangement of multiple representations for science learning.