The invention discloses an intragastric superabsorbent gel primary product and a preparation method thereof, intragastric superabsorbent gel and a preparation method thereof, and a weight reducing composition, and belongs to the technical field of medicines. The structural formula of the hydrogel primary product is as shown in the specification, wherein R1 represents COONa, COOK, CH2OCH2OCOONa orCH2OCH2CH2OH, etc.; R2 is O or NH, etc.; R3 is O, NH, O (CH2CH2O) n4, [CH2CH (OH)] n5 or (CH2CH2) y, etc.,; and R4 is OH, NHCOCH3 or NH2, etc.; and n1 to n5, x and y are integers greater than 0. The hydrogel primary product can increase the satiety of a patient and reduce the weight by reducing the intake, and is high in biocompatibility. The intragastric superabsorbent gel and the weight reducingcomposition also have the above effects, and the weight reducing composition can also avoid the risk that the stomach enters the small intestine to block the small intestine after being emptied. Thepreparation method of the substances is simple and easy to operate.