The normal value of urine specific gravity is between 1.015 and 1.025. Urine specific gravity is the result of using the ratio between urine and water. Factors that affect urine specific gravity include not only the amount of solutes in the urine, but also the size of the solutes. Of course, the most obvious factor affecting urine specific gravity is the amount of water. If the patient sweats more, or has diarrhea that is more pronounced, and does not hydrate accordingly, the urine will be in a concentrated state, and the urine specific gravity will be high. If the patient drinks more water, the urine will increase, which will lead to low urine specific gravity. However, if the patient does not have the above reasons, and drink more water, but the specific gravity of urine is still low, this situation is considered to have a very big relationship with the decline in the concentration function of urine. For example, if the patient takes some drugs for a long time, and these drugs can lead to chronic interstitial damage of the kidneys, such as non-steroidal anti-inflammatory drugs, aristolochic acid and so on, which will affect the concentration function of the kidneys, and the urine specific gravity will be low.