Abstract: Stratified pumping test is a key technique for hydrogeological exploration. To solve the problems of low efficiency and poor reliability and controllability of the traditional water-sealing methods outside casing for stratified pumping, a water-swelling rubber was developed based on high water absorption of the sodium polyacrylate resin, and a new approach based on water-swelling rubber was proposed and optimized by the response surface methodology in this paper. With the water swelling ratio of the rubber as response index, a surrogate model was constructed by the Box-Behnken experimental design to study the influence of different process parameters, working condition parameters, and their interaction on the water-swelling performance. Furthermore, the preparation process of water-swelling rubber was optimized and its working condition was predicted. Optimization results indicate that the optimum combination of working conditions and preparation process parameters of water-swelling rubber includes aqueous solution at pH 7.0, water absorption time of 136 h, sodium polyacrylate 61 phr, and modified aramid short fiber 4.5 phr. Finally, the water-sealing device outside casing was developed, and the feasibility of the proposed method was verified through experiments, which has engineering value for the exploration and utilization of groundwater resources.