The purpose of this study was to identify types of peer feedback that may improve learners’ ill-structured task performance and to develop instructional strategies to use them effectively in peer feedback situation. For the purpose this study incorporated a design-based research in two consecutive semester in phase 1 and 2, respectively. In phase 1, this study found that two types of peer feedback(indicating problems & suggesting solutions) have positive influence on improvement of ill-structured task performance. On the contrary, social message have negative influence on improvement of ill-structured task performance. In Phase 2, instructional strategies for effective use of peer feedback were developed through iterative process of revise and reimplementation. As the results of the iterative process, this study developed a few specific instructional strategies such as using explicit guidance of peer feedback type, visualization and localization peer feedback, and general feedback criteria. Finally, the researcher discussed significance and limitation of this study from the perspectives of design-based research.