In this study the mechanical properties loss and the interface strength of coated AZ31B magnesium alloy (magnesium-aluminum alloy) screws with surrounding host tissues were investigated and compared with naked AZ31B, degradable polymer and biostable titanium alloy screws in a rabbit animal model after 1, 4, 12 and 21weeks implantation. The interface strength was evaluated by the extraction torque to wring out the screws. The mechanical properties loss over time was displayed by one-point bending load loss of the screws after wrung out at different time. Silicon(Si)-containing coating was prepared on AZ31B samples, which effectively decreased the degradation rate of AZ31B and improved its biological properties. The extraction torque of Ti6Al4V, PLLA (Poly-L-lactide) and coated AZ31B increased obviously from 1 week to 4 weeks postimplantation, indicating a rapid osteosynthesis process during the 3 weeks. The extraction torque of coated AZ31B increased with implantation time, higher than those of PLLA from 4 weeks implantation, catching up with that of Ti6Al4V at 12 weeks and higher at 21 weeks. The bending loads of naked AZ31B and PLLA screws degraded sharply after implantion, and that of coated AZ31B degraded more slowly. The biodegradation mechanism, the coating to control the degradation rate and the bioactivity of magnesium alloys influencing the mechanical properties loss over time and bone-implant interface strength were discussed in this study and it is thought that a proper degradation rate will make the corrosion biodegradation mechanism and the bioactivity of magnesium alloys more beneficial for the mechanical performance and their application in clinic.