The causes of polyuria are mainly classified as physiological and pathological. Polyuria generally refers to a daily urine volume of more than 2,500 ml in 24 hours. Physiological polyuria can occur in normal people when they drink a lot of water or eat too much food containing a lot of water, which is normal. Persistent polyuria is pathological, and the cause needs to be clarified and treated in a timely and symptomatic manner. The main causes of pathological polyuria are endocrine diseases and kidney diseases. Endocrine diseases such as diabetes mellitus, uremia, hypokalemia, etc. can cause polyuria. Renal diseases such as polyuria in acute renal failure, early stage of chronic renal failure can also show nocturia and tubulointerstitial nephritis. Polyuria can also occur in certain specific diseases that require treatment with mannitol. It is especially important to improve urinary routine, urine glucose and blood glucose measurement, and blood biochemical examination after polyuria occurs. In summary, there are many reasons for polyuria, and once it occurs, it is recommended to seek medical attention, improve the relevant tests, clarify the diagnosis and provide timely and symptomatic treatment.