Based on the relevant theories of project-based learning, taking "Utilization and Loss of Water" as an example, we design and carry out interdisciplinary project-based teaching activities for junior high school biology; by creating life-like situations, we promote students" construction of biological concepts, Internalize and apply, improve their ability to apply knowledge across disciplines, practice hands-on practice and analyze and solve problems in real situations, and promote the overall development of core competencies in the discipline.