Transcranial Doppler ultrasound, also known as TCD, is a common clinical method for the detection of cerebrovascular disease, using the effects of ultrasound Doppler to examine the arterial hemodynamics and physiological parameters of blood flow in the patient’s brain. Transcranial Doppler is mainly used to assess the state of blood flow by the level of blood velocity, and it can be used to do preliminary screening for some diseases. The advantages of transcranial Doppler are that it is non-invasive and easy to examine, and it can be used for the initial screening of some diseases. The scope of transcranial Doppler is mainly for obstructive diseases of intracranial vessels and obstructive lesions of extracranial vessels, especially the pressure neck test can be used to understand whether the patient has good collateral circulation, to evaluate the extracranial segmental vascular diseases, such as whether there is blood steal from the subclavian artery and the effect on intracranial blood flow, and also to identify the effect of blood flow. It is also possible to identify the blood supply of venous malformations.