In recent years, point of care ultrasound (POCUS) has developed rapidly in the fields of anesthesia and critical care. POCUS is widely used in clinic to monitor the function of human tissues and organs such as the heart, lungs, and diaphragm due to its visual, non-invasive, portable, and repeatable characters at the bedside. Diaphragm is an important structure to maintain respiratory function. Diaphragm paralysis or dysfunction can cause a significant decrease in inspiratory function. The patient's diaphragm function can be assessed through monitoring diaphragm thickness and activity by POCUS, and combined with other clinical indicators, the patient's recovery of respiratory function can be comprehensively evaluated, and rapidly identify the pathological conditions, such as diaphragm paralysis, diaphragm atrophy, diaphragmatic hypoplasia and amyotrophic lateral sclerosis. Dynamic evaluation of the process from diaphragmatic dysfunction to recovery can provide guidance for weaning and extubation, and real-time feedback on the treatment effect. This article reviews the ultrasound evaluation methods and clinical applications to the diaphragm, in order to guide clinicians to use relevant indicators to comprehensively evaluate the structure and function of the diaphragm, and then diagnose and treat diaphragm dysfunction, which may help making clinical decision.