For obese people who were not suitable for strenuous exercise, a magnetic control slimming capsule model that could complete the process of inflating and deflating in the stomach was proposed. The capsule was inflated by the acid-base salt reaction, and the inflated balloon occupied the internal gastric volume in the stomach to achieve the purpose of weight loss. The occurrence of the chemical reaction was controlled by small magnets inside, and the driving of small magnets could be controlled by an external magnet. After the treatment was over, the balloon was deflated by the external magnet and the capsule could be discharged naturally from the digestive tract. Combined with chemical experiments, the reaction scheme was determined as a saturated solution of citric acid monohydrate reacting with sodium bicarbonate powder, and the volume of the solution was controlled at 2 mL. The finite element simulation analysis of the magnet model was carried out by COMSOL Multiphysics software, and the volume of the magnet outside the capsule was estimated. The results revealed the reaction mechanism of the proposed capsule structure model and proved its feasibility.