Abdominal pain is one of the common symptoms in the gastrointestinal tract and has a complex etiology. Patients with lesions in the upper gastrointestinal tract or large intestine can generally identify the cause after gastroscopy, colonoscopy, abdominal ultrasound, abdominal CT and routine hematological examination, while abdominal pain due to small intestinal lesions is not easily diagnosed because of the low specificity of symptoms and the deep and variable location of the lesions, which is one of the common causes of unexplained abdominal pain. Capsule endoscopy is simple, non-invasive and painless, and has a high detection rate, which is widely recognized by physicians and patients. In this paper, we retrospectively analyzed 103 patients with unexplained abdominal pain admitted to our hospital from May 2013 to May 2015. In order to evaluate the value of capsule endoscopy in the etiological diagnosis of patients with unexplained abdominal pain. 1. Data and methods 1.1 General data All 103 patients had no contraindications to capsule endoscopy, such as gastrointestinal obstruction, perforation, fistula, etc., and their clinical manifestations were recurrent abdominal pain, and the causes of abdominal pain were not clearly identified by routine gastroscopy, ultrasound and CT examination. Among them, 48 were male and 55 were female; age ranged from 18 to 92 years, with an average of 45.14 years. The history of abdominal pain ranged from 5 months to 10 years. All patients signed the informed consent. 1.2 Examination method The OMOM capsule endoscope of Chongqing Jinshan Company was used. The system consisted of three parts: OMOM capsule, data recorder and imaging workstation. All examiners had a full liquid diet for dinner the day before the capsule was swallowed. After 20:00, the bowel is cleansed with polyethylene glycol electrolytes from 7:00 am on the day of the examination. Simethicone oil is taken orally 30 minutes before the examination. Patients who did not pass through the pylorus were given intraosseous metoclopramide and fasted for 2 h after swallowing the capsule. After 9 h, the recorder was removed and the information from the recorder was downloaded to the imaging workstation. The capsule was expelled at the end of the digestive tract operation and was for single use. 1.3 Statistical treatment SPSSl7.0 statistical software was used. The X2 test was used for the count data, and P<0.05 was considered a statistically significant difference. 2. Results 2.1 Examination procedure In 103 cases, except for 1 case (0.97%) in which the capsule endoscope was retained in the small intestine during the 9-hour examination period, the remaining 102 cases (99.03%) all completed the small intestine examination, and all expelled the capsule endoscope on their own without any obvious adverse effects. The capsule endoscope was embedded in the jejunum and was removed by double balloon small intestine microscopy. Meanwhile, the biopsy pathology reported granulomatous hyperplasia with inflammation. It was consistent with Crohn's disease. In two other cases (1.94%), the capsule did not pass through the pylorus after two hours and was delivered into the duodenum by transoral gastroscopy. 7 hours later, the capsule was observed to have entered the colon by imaging workstation. 3. Discussion Capsule endoscopy was applied to clinical practice in 2001, and the early studies mainly focused on the diagnosis of unexplained gastrointestinal bleeding, but less on the application of abdominal pain. In the present study, the detection rate of small bowel disease by capsule endoscopy was 66.99%, in which small bowel erosion was found to be the most common (41.75%), followed by small bowel Crohn's disease (8.73%), which is consistent with domestic studies. Crohn's disease is an inflammatory bowel disease, mostly occurring in the small intestine, and the incidence has increased year by year in recent years, probably related to the increasing improvement of small intestinal examinations such as capsule gastroscopy and double balloon small intestinal microscopy. Endoscopically, longitudinal ulcers, pavement-like changes, segmental, and often tubular stenosis are seen. 5 patients with small bowel capillary dilation were associated with overt or occult bleeding, and these patients had intermittent vague abdominal pain or discomfort. Small bowel capillary dilation is a vascular disease of the small intestine, which can be treated endoscopically, medically, or surgically, but is prone to recurrence. Thirty-four patients (33.01%) with undetected disease were considered to have irritable bowel syndrome, as they were mostly accompanied by altered bowel habits after asking for medical history. The completion rate of the capsule was 99.03%, and retention occurred in one case, which was removed by double balloon small bowel microscopy. Capsule retention is one of the major complications of capsule endoscopy and has numerous causes, such as diabetes, gastrointestinal dysmotility, and intestinal stricture [4]. In this case, the capsule was retained due to small bowel stricture caused by Crohn's disease. Capsule endoscopy is simple, visual, non-invasive, safe, single-use, non-cross-infected, well tolerated by patients, and has a high diagnostic value for small bowel diseases. However, it also has some limitations, as it cannot control the lens, depends on the patient's gastrointestinal motility, cannot be biopsied, and cannot be treated endoscopically. Therefore, as a diagnostic tool for abdominal pain of unknown origin, in addition to capsule endoscopy, if it can be combined with multilayer spiral CT small bowel imaging and double balloon small bowel microscopy, the diagnostic rate can be further improved and therapeutic work can be carried out.