Objective　To compare the stability and stress distribution of titanium alloy and magnesium alloy Jefferson-fracture reduction plate(JeRP) system for fixation of unstable Jefferson fracture.　Methods　The spatial structure information of atlas was obtained through CT scanning, and the geometry model of JeRP system for t fixation of unstable Jefferson fracture was established in Solidworks system. The internal structure changes, and the stress distribution of titanium alloy and magnesium alloy JeRP system and atlas were imitated and analyzed in Ansys13.0 system under physiological load in neutral, anteflexion, extension, lateral bending and rotation positions.　Results　(1) There were high geometric similarity and qualified stress distribution on the finite element model of JeRP system for fixation of unstable Jefferson fracture. (2) In different positions under physiological load, the stress of JeRP system was located mainly at the mid-part of the JeRP, the root and top of screws in anteflexion and extension position and, at the mid-part of screws in lateral bending position. (3) The maximum stress of JeRP system was less than the yield strength of titanium alloy and magnesium alloy under physiological load. The elastic strain of JeRP system and deformation of fracture were quite small. The fracture surface stress of magnesium alloy group was larger than the titanium alloy group.　Conclusion　Both the titanium alloy and magnesium alloy JeRP system have enough strength and effect of fixation for the treatment of unstable Jefferson fracture in physiological load, but magnesium alloy JeRP system is better than titanium alloy JeRP system in promoting fracture healing.