Project-based learning (PjBL) facilitates STEM learning, but the integrity of the project activities is a challenge and the design of integrated STEM courses through PjBL remains unclear. The purpose of this study was to design and evaluate a transdisciplinary STEM course integrated through PjBL in robotics. Participants in the teaching experiment for four weeks were 54 high school students, including 29 males and 25 females. Based on semi-structured interviews with students and teachers and open-ended questionnaires from students, the course not only facilitated knowledge integration and application but also brought a positive effect on students' learning outcomes. This study not only confirms that PjBL can be applied in the STEM course but also provides a practical example as a reference for designing transdisciplinary STEM courses integrated through PjBL. Finally, the implications for teaching practices and theories are also proposed.