The ability to solve real-world problems for a sustainable future has become a worldwide consensus, and interdisciplinary competencies and project-based learning (PBL) have become the focus of curriculum reform in China. This study investigates the effectiveness of interdisciplinary PBL fieldwork in geography education for sustainable development, focusing on the perceptions of students from a junior high school in Chongming, Shanghai, of the interdisciplinary effectiveness of PBL fieldwork. Over a one-month pilot program, the results suggest that the new fieldwork approach did not achieve the expected benefits. The significant gains of students can be grouped into four perspectives, namely, understanding of nature and classroom knowledge; problem-solving skills and environmental action; scientific spirit, environmental awareness, and interest in geography; and understanding of local needs and sustainable development issues, which increased their interest in learning. The students generally accepted the ability to collect information and data and the thinking ability of circular development. The influencing factors of activity effectiveness include the time and difficulty of the activity, cognitive and knowledge levels, learning habits of students, student participation, and teaching experience of teachers. The study offers valuable insights for improving fieldwork in other regions and for future research.