With the clinical application of hemodialysis, real-time monitoring of patient’s blood volume has become an important work for dialysis machine in recent years. Blood volume monitoring can provide the information of relative blood volume in patient, which has a vital clinical significance in understanding the patient’s hydration state, preventing symptomatic hypotension and refractory hypertension, adjusting dry weight, and making dialysis solution. In this paper, we mainly introduce several blood volume monitoring methods and the application value of blood volume monitoring in the clinic. At the same time we point out the existing problems and the research direction of blood volume monitoring in the future.