The purpose of this study was to use the Metacognition-Based Dynamic Assessment (MBDA) to generate a teaching model in order to investigate the 3rd grade students’ mechanism of conceptual change on “Air”. This study focused on 28 students to gather relevant information and then chose 12 students from them to perform 4 individual interviews. Finally, selected 3 of the students to perform postponed interviews. The information gathered was mainly used for quality analysis, and the results as well as findings from this research were clarified as below: 1. Student’s Conception before Learning of Air Students’ pre-conception could be divided into four categories, including: “Conforming to the correct scientific concept”, “The incongruence between depiction and recognition”, “A alternative frameworks”, and “The wrong answer and cause depiction for questions”. 2. Science Conceptual Change Mechanism and Levels The differences among levels from the lowest to the highest could be categorized as: Observation Level�Realization Level�Knowledge Level�Application Level. 3. Students Review the Processes of Conceptual Change Students’ metacognition about “Air” could be categorized into 8 categories. 4. The Important Findings From Students’ Postponed Interview Within the concept learning, the quality of conceptual change could use an analogy of the chemical collision theory with its influence including: The pre-concept for students’ learning (Reactant nature), The ability for metacognition (Temperature), The context arrangement for course teaching (Condensation), MBDA (Catalyst).