Oliguria is a significant decrease in the patient’s urine output, which is considered to be oliguria when the total urine output is less than 400 ml in 24 hours in clinical medicine. At this point, relevant laboratory tests are needed to clarify the cause of oliguria. Under normal circumstances, the human body urinates about 1000-1500ml per day. If there is insufficient fluid replacement or increased sweating, etc., the urine volume may be less than 1000ml or less. However, if the kidneys are not pathologically diseased, the urine volume is usually above 400ml. If the kidneys develop related disease and there is a decrease in filtration capacity, this will produce a decrease in urine volume. For patients who are clinically monitored to have a 24-hour urine volume of less than 400ml, it is necessary to perform renal function tests, filtration function tests, etc. to assess the degree of kidney damage. Active and effective treatment is needed to avoid irreversible kidney damage.