The blended composites with ultra-high molecular weight polyethylene (UHMWPE) as the matrix polymer, sodium polyacrylate (PAANa), and tetraphenyltin (Ph4Sn) as fillers were prepared by hot compression molding process. The friction and wear behavior of GCr15 balls with composites mating pairs under the seawater environment was explored, and the friction and wear mechanism was analyzed. The results show that adding PAANa, a polyelectrolyte material, can effectively reduce the friction coefficient of UHMWPE/PAANa/Ph4Sn composites. The wear resistance of composites increased significantly with increasing Ph4Sn content compared with pure UHMWPE, and the best wear resistance was observed at 1% content. The primary wear mechanism of UHMWPE/PAANa/Ph4Sn composites changed from adhesive wear of pure UHMWPE to plastic deformation at lower PAANa and Ph4Sn contents and finally to adhesive wear and spalling. This work provides a theoretical basis for preparing and applying other polymer blend composites.