Slow-releasing oxygen materials were prepared to overcome some limitations regarding the low dissolved oxygen (DO) concentration and the low efficiency of in-situ purification in groundwater. Tests on slow-releasing oxygen materials that could be used to change the reductive environment in groundwater by slowly releasing oxygen were carried out. Oxygen-releasing laboratory experiments were conducted to monitor changes in DO concentration, pH, and total dissolved solids (TDS) in aqueous solutions. The adsorption of the materials on total Fe and Mn were also analyzed. The experimental results showed that the oxygen-releasing status of materials was stable at 15 mg/L after 20 d for fixed-shape materials. Paraffin wax shells and a KH2PO4 pH regulator facilitated the lowering of pH. The oxygen-releasing process followed the quasi-second-order kinetic model, and the oxygen-releasing rate constant K was 1.28, 1.51, and 1.97 (mg/(L·h)) for silt, silty sand, and fine sand medium, respectively. The larger the seepage medium particles were, the faster the pH and TDS dropped. Adsorption experiment results showed that adsorption on total Fe and Mn were well simulated by the Langmuir nonlinear isothermal adsorption equation. The maximum adsorption capacities of the materials on total Fe and Mn were found to be 0.708 mg/g and 0.438 mg/g, respectively.