With the purpose of decreasing production costs and mitigating negative effects on the environment, an ecofriendly superabsorbent composite (SB@PDA/PAA) was synthesized by grafting poly(acrylic acid) onto the surface of dopamine-coated waste sea buckthorn branches. The structure of the obtained products was analyzed using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The effects of pH level, salt concentration, cation type, and reswelling time on water absorbency were examined further. The results showed that the swelling behaviors of the superabsorbent composite were highly sensitive to the concentration of salt solution, cation type, and reswelling time. The swelling kinetics of SB@PDA/PAA in distilled water could be fitted well with a pseudo-second-order kinetic model. Moreover, the SB@PDA/PAA superabsorbent composites exhibited excellent water-retention properties and achieved a high degradability of 33.5 wt % when they were soaked in a soil solution for 90 days. On the basis of these investigations, it is believed that the obtained SB@PDA/PAA could have potential applications in agricultural or industrial areas because of their water superabsorption and retention capacities, high reswelling capability, and cost-effective and ecofriendly preparation and use. The proposed technology can also be extended to the synthesis of other natural biological resources and organic hybrid materials with similar structures.