In patients with acute renal failure polyuria phase, the urine volume can reach 3000-5000ml, and the polyuria phase will be relieved after it lasts 1-3 weeks. The reason for the polyuric phase of acute renal failure is that the glomerular filtration rate has returned to normal during the polyuric phase, but the function of the renal tubules has not yet returned to normal. The renal tubules have the function of concentrating urine and are able to absorb most of the water as well as substances. If the tubular function is not restored, the original urine filtered from the glomerulus cannot be completely reabsorbed back into the body, and this will lead to polyuria. It is also important to rehydrate appropriately during the polyuric phase and to monitor electrolytes closely, as the polyuric phase often causes electrolyte disturbances.