Due to the lack of process and easy-to-learn system-level diagnosis methods for a chiller plant. The authors of this article presented an energy-saving diagnosis strategy for chiller plants to detect faults early and achieve sustainable built environments. This strategy analyses common weaknesses in building chilled water systems from maintenance, design, and operation perspectives. It comprises four steps: macroscopic energy efficiency index judgment, system troubleshooting, design diagnosis, and operation diagnosis. The authors applied the strategy to a typical hospital building in a hot and cold region of China. They found that partial-load conditions were a significant problem, reducing cooling efficiency and excess cooling in unoccupied rooms. The overall yearly energy efficiency (𝐶𝑂𝑃𝑝𝑙𝑎𝑛𝑡) was 3.27, and the useless energy consumption caused by this operation in 2021 is as high as 510327 kWh. A specific solution was proposed, including replacing the check valve, cleaning the condenser, and avoiding multiple water pumps with a small number of hosts. The authors also recommended developing a frequency conversion control strategy for the water pump under partial load and creating a chiller opening strategy at different load intervals of the building.