Acute tubular necrosis (ATN) is the most common type of acute renal failure, accounting for approximately 75% to 80% of cases. It is a clinical syndrome that occurs as a result of acute, progressive decompensation of renal function due to renal ischemia and/or nephrotoxic damage caused by various etiologies. The main manifestations are progressive azotemia due to a marked decrease in glomerular filtration rate, and imbalance of water, electrolyte and acid-base balance due to low renal tubular reabsorption and excretion function. In terms of differential diagnosis, pre-renal oliguria and post-renal urinary tract obstruction should be excluded first, and when the renal substance is identified, it should be distinguished from glomerular, renal vascular or interstitial renal lesions. The patient has a history of volume deficiency or cardiovascular failure, and the degree of azotemia in simple pre-renal failure is not serious, the urine volume increases after blood volume supplementation, the blood Cr returns to normal, the urinary routine changes are not obvious, the urine specific gravity is above 1.020, the urine osmotic concentration is greater than 550 mOsm/kg, the urine sodium concentration is below 15 mmol/L, the urine, the blood creatinine and The ratio of urine, blood creatinine and urea nitrogen are above 40:1 and 20:1, respectively, but in elderly cases with simple prerenal failure, if the original renal function is impaired, it also reflects the change of renal parenchymal failure. 2. Differential diagnosis with post-renal urinary tract obstruction A history of urinary stones, pelvic organ tumor or surgery, sudden complete anuria or intermittent anuria (ureteral obstruction on one side and renal insufficiency on the opposite side may be manifested as oliguria or non-oliguria), renal colic and percussion pain in the renal area, no significant change in urinary routine, B-type ultrasound urological examination and urinary X-ray examination can often make a quicker differential diagnosis. 3, and severe acute glomerulonephritis or acute glomerulonephritis differential diagnosis severe nephritis early often have obvious edema, hypertension, large amounts of proteinuria with obvious microscopic or carnal hematuria and various tubular and other glomerulonephritis changes, there are difficulties in the diagnosis, the proposed treatment with immunosuppressive drugs should be done to clarify the diagnosis of kidney biopsy. The differential diagnosis with acute interstitial renal lesions is mainly based on the cause of acute interstitial nephritis, such as drug allergy or history of infection, obvious pain in the kidney area, drug-induced fever, rash, joint pain, blood eosinophilia, etc. It is sometimes difficult to differentiate this disease from ATN, and a renal biopsy should be done first, and most acute interstitial nephritis requires treatment with glucocorticoids. Renal biopsy is important for the identification of the cause of acute renal failure, and sometimes some diseases that are not considered in the identification can be found through renal biopsy.