The specific etiology of sudden oliguria needs to be analyzed according to the condition. Clinically, it is considered that a 24-hour urine volume of less than 400mL is meaningful oliguria and requires further examination. If the 24-hour urine volume is indeed less than 400mL, it is considered oliguria, and possible etiologies include: i. Acute renal failure, where various causes cause the kidney function to stop filtration and result in body fluids not being able to be filtered out through the kidneys, and the patient’s urine volume decreases, often seen in acute poisoning, traumatic injury or acute progressive exacerbation of chronic renal failure. In addition to oliguria, it may also be accompanied by hypertension, edema, large amounts of proteinuria, swelling, etc. Treatment requires kidney dialysis treatment or transplantation and other treatments to completely cure. Second, posterior renal obstruction due to acute stones, tumors and other causes, that is, the filtration function of the kidneys is normal, but the urine filtered by the kidneys cannot be excreted through the ureteral bladder and urethra. The causes that affect urination are bilateral ureteral stones, urethral stones, bilateral ureteral tumors or intra-abdominal tumors that compress the ureter, such as gynecological tumors that cause bilateral ureteral invasion, resulting in oliguria because the kidneys cannot produce urine to drain out of the body. This situation requires further examination to determine the obstructing factor and then remove the obstructing factor in order to restore normal urination. Third, physiological decrease in urine volume, such as less water consumption and more sweating, is commonly seen in cases of heat stroke or ischemic shock, coma, etc. in hot weather. This situation is relatively good, that is, there is no role of kidney filter damage, only rehydration, infusion, hydration to restore normal urine, it is recommended to go to the hospital for further examination to clarify the causes of oliguria and targeted treatment.