Acute renal failure, except for a small number of polyuric type, most of them go through 3 stages of oliguria, polyuria and recovery, especially acute tubular necrosis is more typical. Oliguria: It means that the urine output is less than 400 ml in 24 hours, or less than 17 ml per hour, and usually lasts for 1~2 weeks, but there are cases that last for more than 4 weeks. The main manifestations of water intoxication, metabolic disorders such as electrolyte disorders, acid-base balance disorders, uremia. Water intoxication is often manifested as generalized edema, or even pulmonary edema, cerebral edema, congestive heart failure, etc. Electrolyte disorders commonly include high blood potassium, low blood sodium, low blood calcium, high blood magnesium, etc. Acid-base balance is mainly manifested as metabolic acidosis. The simultaneous presence of heat-negative balance can exacerbate acidosis and uremia. Uremia is characterized by a rapid increase in BUN, Scr, and gastrointestinal reactions such as nausea, vomiting, and loss of appetite. As a result of these various pathophysiologic changes, it is often easy to complicate pulmonary infection, cardiac arrhythmia, neurological damage, and even lead to death. Polyuria: After the oliguria period, renal blood flow and glomerular filtration rate increase, and polyuria begins to occur, entering the polyuria period, but it does not mean that it has been recovered, because at this time azotemia still exists, and the tubular concentrating function has not been restored. There are still water electrolyte disorders. The performance of the 24-hour urine volume increased to more than 1500 ml, more than 6000 ml, of course, the daily urine volume is gradually increased, as long as the daily urine volume of 400 ml or more, that is to say, the beginning of the polyuria period. The duration of polyuria is about 7~14 days. Polyuria indicates the beginning of recovery of renal function, with the increase of urine output, the various disorders of oliguria are gradually improved. However, it is also easy to have negative balance of water and electrolytes, such as dehydration, low blood potassium, low blood sodium, or high blood calcium, at the same time, due to long-term consumption, the patient’s resistance decreases, and it is easy to complicate infection. Recovery period: After the polyuria period, it enters into the recovery period, which varies in length according to the patients, and usually lasts for 3 months to 12 months. In this period, renal tubular dysfunction often exists, and most of them can be completely restored to normal, and only a few of them can have residual renal insufficiency and develop into chronic renal insufficiency.