The critical elderly patients are usually frail with multiple degenerated organs and comorbidity of chronic diseases, characterized by different clinical manifestations, severe conditions, rapid progression, and high mortality. In recent years, bedside ultrasound has become an important visualized examination method for its advantages of non-invasiveness, convenience, speed, non-radioactivity and real-time dynamic checks, repeatability, and integrative examination of multiple spots. This paper reviews the application of bedside ultrasound in elderly patients with critical illnesses in cardiovascular, respiratory, urinary, and digestive systems.