Urea is mainly synthesized in the liver, and is a product of protein metabolism in the human body. It is synthesized in the liver with carbon dioxide after the breakdown of amino acids, and enters the bloodstream through the kidney filtration and is excreted with urine, and a small portion will be excreted with sweat. The role of urea is mainly manifested in eliminating the metabolic waste ammonia from the body and allowing it to be excreted in the form of urea. Urea in the renal tubules enters the renal cortex and helps the renal cortex to use the osmotic pressure to facilitate the recycling of water from the renal tubules to the interior of the body. Urea level is one of the main indicators to evaluate kidney function. By monitoring the level of urea in blood through laboratory, it may be possible to initially determine whether the filtration function of glomerulus is normal, and to make staging guidance for patients with chronic renal insufficiency according to the increased level of urea in blood, and to make a proper assessment of the treatment effect of patients.