Objective: To investigate the effect of different dosage forms of defoamer and different administration time on the clarity of gastric visual field of children's magnetically controlled capsule endoscopy. Methods: Retrospective analysis was made on 180 children who received magnetically controlled capsule endoscopy examination in Children ‘s Hospital Of Shanghai from January 2017 to March 2023. They were divided into dimethicone powder group, dimethicone emulsion group, and simethicone emulsion group according to the type of defoamer taken, and further divide into 30min, 45min, and 60min groups based on the time taken before examination. The main evaluation indicator was the gastric bubble score, and secondary evaluation indicators included gastric cleanliness score, gastric examination time, gastric transit time（GTT）, diagnostic efficacy, and safety evaluation. Results: The gastric bubble score and gastric cleanliness score of the 45 minutes group treated with dimethicone powder group were significantly lower than those of the other groups, with higher clarity and statistical significance (P<0.05). There was no statistical difference in gastric examination time, gastric transit time, and positive detection rate of gastric diseases among the groups (P>0.05). Conclusions: Taking defoamer before magnetically controlled capsule endoscopy can significantly reduce bubble in the stomach and increase the clarity of gastric mucosa. It is better for children to take 5g dimethicone powder dissolved in 30ml warm water 45 minutes before stomach examination.