If the urine is small and yellow, then the possible causes: First, when the urine is concentrated, there can be a decrease in urine volume and yellow urine color, because of less water consumption, resulting in insufficient body fluid or more sweating, or there is vomiting, diarrhea and other reasons that lead to dehydration of body fluid, there will be insufficient filtration of the kidneys and produce less urine, and accompanied by yellow urine color. Generally, after drinking more water or replenishing water, the urine volume can be restored. Secondly, when urinary system infection occurs, there can be an increase in the pigment in the urine and the increase in bacterial products and metabolites, which can be manifested as cloudy urine, yellowish color, accompanied by low urine output but increased frequency of urination. Patients mostly have urinary frequency, urinary urgency, back pain, fever and other symptoms, need to carry out routine urine examination, urine culture examination for further identification. Third, when suffering from kidney disease, such as glomerulonephritis, acute nephritis, etc., can cause the kidney filtration deficiency, appearing urine volume reduction and yellow color. At this time, routine urine examination, there is also a large amount of proteinuria visible in the urine, further kidney function tests are needed to clarify, usually this condition of oliguria, urine volume are less than 400ml or less in 24 hours.