Diaphragm dysfunction is associated with prolonged ICU stays, weaning failure, and increased mortality, so timely assessment of diaphragm function is critical for patient outcomes.In the past, fluoroscopy, MRI, electromyography of diaphragm, transdiaphragmatic pressure and other methods were used to evaluate diaphragm function, but the use was limited due to radiation, invasive, complex operation and other reasons.As a real-time, non-invasive, non-radiative, economical, qualitative and quantitative examination method, ultrasound can be widely used in the monitoring of bedside diaphragm function. This article reviews the physiological characteristics of diaphragm, parameters of diaphragm function evaluation by ultrasound and clinical application.