Earth’s health condition is getting worse due to global warming, urbanization, and desertification, significantly threatening the ecological security and the sustainable development of society. The land that cannot produce adequate oxygen through photosynthesis will gradually lose water storage capacity, resulting in positive feedback that warming and drying reinforce each. By regarding the Earth as a living body, we propose the concept of land cancer and develop a method to diagnose its health condition. Also, we constructed the cancer land index (CLI), which indicates that cancerous land accounts for 53% of the global land area. Land cancer starts from deserts and drylands with the lowest oxygen production, and from urban centers and concentrated industries with the highest oxygen consumption, then gradually expands to the surrounding areas. The whole process is analogous to the spread of cancer cell in the human body, manifesting the deterioration of Earth’s health. Our study thoroughly investigates the concept of land cancer and detects areas of cancerous lands, which offer mitigation suggestions for natural and anthropogenic cancerous lands. The
objective is to strive for early detection of land cancer and prevent its expansion, thereby protecting Earth’s health.