Normal human urine production is primarily through the filtration of the glomerulus and the reabsorption and secretion functions of the renal tubules. Hemofiltration is designed to mimic this filtration principle of the renal unit, but without the reabsorption function of the renal tubules. The treatment process requires replenishment of large amounts of fluid with similar composition to extracellular fluid to replace the function of the renal tubules. The main difference between hemofiltration and hemodialysis is that hemofiltration removes solutes by convection, whereas hemodialysis removes solutes by diffusion. The former is similar to the principle of solute removal by normal glomeruli and has equal ability to remove medium and small molecules, while hemodialysis has better clearance of small molecules such as urea and creatinine, while it has poorer clearance of medium molecules. Hemofiltration is performed by introducing the patient’s arterial blood into a semi-permeable membrane filter with good permeability and an area comparable to that of the glomerular filtration membrane. Due to the transmembrane pressure gradient between the blood area and the outer membrane, when the blood passes through the filter, water and most of the small and medium molecules are filtered out of the plasma, except for the organic components such as proteins and cells, in order to achieve the therapeutic purpose of removing excessive water and solutes retained in the blood. Hemofiltration is suitable for the following conditions 1. Intractable hypertension: Patients with intractable hypertension that cannot be controlled by drugs and hemodialysis have normalized their blood pressure after applying hemofiltration. It may be related to the removal of certain pressurizing substances from the plasma during hemofiltration. It may also be related to the fact that the cardiovascular system and extracellular fluid are more stable during hemofiltration, which reduces the stimulation of the renin-angiotensin system. 2. Water retention and hypotension: In patients with water retention with hypotension, it is not possible to eliminate enough water through hemodialysis because hypotension and deficiency occur early in dialysis. In these patients, the manifestations of circulatory disturbances are significantly improved if hemodiafiltration is switched. The main advantage of hemofiltration is the ability to remove large amounts of fluid without causing hypotension. 3. Hypervolemic heart failure: This type of patient is often aggravated during hemodialysis, while hemofiltration can reduce or treat this type of heart failure because ① hemofiltration can rapidly remove excess water and reduce the preload of the heart. ② Although dehydration is effective and reduces blood volume, it is isotonic dehydration, which increases peripheral vascular resistance and maintains blood pressure stability. ③After removing a large amount of water, the plasma albumin concentration increases relatively, which facilitates the entry of water from the surrounding tissues into the blood vessels and reduces edema. ④No need to use acetate dialysis solution, which avoids the resulting vasodilation and inhibition of cardiac contractility. Because of all these advantages, hemofiltration is an effective treatment for patients with cardiac insufficiency who do not respond to diuretics. Although hemofiltration has its advantages, its use also has its disadvantages: (1) high cost due to the need to replenish a large amount of replacement fluid. ②Volume balance is out of balance. If the filter does not have an automated volume balancing device and relies on manual operation, either insufficient volume produces hypotension or excessive volume increases cardiac load. ③The removal of small molecules is poorer than hemodialysis.