Objective To evaluate the biomechanical stability of pectin/polyvinyl alcohol composite （CoPP）hydrogel and to assess the range of motion(ROM) and intradiscal pressure (IDP) changes at the above adjacent segment after the anterior implantation of CoPP hydrogel and cage. Method Six fresh cadaveric lumbar spine specimens（L3～L5）were biomechanically tested on the robotic testing machine. ROM at L3/4 and L4/5 and intradiscal pressure at L3/4 were measured. All measurements were made with initially intact and followed by both CoPP and cage implantations. Results At the implanted level (L4/5), the CoPP spine showed no significant change in the other five motion directions except left lateral bending motion compared with the intact spine (P>0.05), whereas the cage spine decreased significantly in all motion directions when compared with the intact spine or CoPP spine (P<0.05). At the above adjacent level of L3/4, the CoPP revealed a minor change in all motion directions except left lateral bending motion compared with the intact spine (P>0.05), whereas the ROM of cage spine significantly increased in all motion directions compared with the intact spine (P<0.05). The IDP of the CoPP spine did not increase under any condition compared with the intact spine (P>0.05). While the IDP of cage spine significantly increased in flexion/extension and left/right lateral bending compared with the intact spine or CoPP spine (P<0.05). There was no significant increase in axial rotation compared with the intact spine or CoPP spine (P>0.05). Conclusions The implantation of CoPP prosthetic nucleus can preserve the motion function at the operated level and maintain the lumbar stability. Compared with the lumbar fusion, the nucleus replacement has no significant effect on the ROM and IDP at adjacent level, which may decrease or avoid the adjacent segment degeneration.