The normal value of urine specific gravity is between 1.003 and 1.030. For normal people, they should drink more than 2000ml of water per day and their urine is at normal urine specific gravity. For urine specific gravity is lower, less than 1.003, it may be the polyuric phase of renal failure or uremia, which will excrete a large amount of urine with low urine specific gravity. For urine specific gravity greater than 1.030, we should pay attention to whether the urine is concentrated due to low water consumption. After the urine is concentrated, the urine specific gravity increases significantly, which may lead to an increased incidence of infection and stones.