It is a clinical syndrome of nutrient deficiency caused by various causes of impaired digestion and absorption in the small intestine, resulting in failure to absorb nutrients normally and excretion in the stool, also known as malabsorption syndrome. Because the patient has diarrhea, thin stool and large amount, and contains more fat, also known as steatorrhea. The examination methods of steatorrhea are as follows. 1, fecal examination including appearance, microscopic examination and culture. Microscopic examination pay attention to the presence of red blood cells, white blood cells, eggs, protozoa, etc., Sudan III staining can be checked for fat droplets. The fungal examination and fungal spectrum analysis of stool can help the etiological diagnosis of diarrhea. 2, microscopic examination of fecal fat (1) put a small amount of feces on the slide and Sudan III saturated solution 1 to 2 drops mixed microscopic examination, can be seen in the neutral fat vermilion round oil droplets; free fatty acids are dark yellow-red bundle needle-shaped, or short thin curved needle-shaped crystals; and combined fatty acids are not colored, pile needle-shaped or arranged in a fan shape. (2) Take one drop of saline and one drop of saturated alcohol solution of scarlet dye, add a little feces on the slide and mix well, cover with a coverslip for microscopic examination. Round vesicle-shaped neutral fat and crystalline fatty acids can be seen. If more than 1/4 of the specimen is dyed red, the test is strongly positive (ten ten or ten ten ten), and it is heavy steatorrhea. 3.Quantitative determination of fecal fat is generally determined by Vandekamer method, test method: eat standard meal (containing fat 60-100g/day) for 3 days continuously, and measure the amount of fecal fat for 3 days at the same time. Take the daily average, if the amount of fecal fat >6g per day, or fat absorption rate <95%, can be considered to have fat malabsorption. 4, absorption function test D-xylose absorption test, vitamin B12 absorption test, pancreatic function test, etc. 5.Other auxiliary examinations Blood routine, blood sedimentation, electrolytes, urea nitrogen, carbon dioxide binding capacity, etc. If gastrogenic diarrhea is suspected, gastric fluid analysis should be performed. For patients suspected of hyperthyroidism, relevant tests such as basal metabolic rate, thyroid iodine uptake rate, etc. should be done. Pancreatic function tests, imaging and endoscopy can assist in the diagnosis of primary diseases of the pancreas and gastrointestinal tract that cause steatorrhea.