ObjectiveTo study the biomechanical impact of two different kinds of odontoidectomy on the stability of cervical junction through a validated finite element model of Oc-C2.MethodsA validated finite element model of Oc-C2 was constructed to study the biomechanical changes due to the surgery of traditional odontoidectomy and odontoidectomy with anterior C1 arch preservation. These models were analyzed in ABAQUS v6.9.1. to study the biomechanical impact of anterior C1 arch preservation.ResultsOdontoidectomy produced more motion increase at C1-C2 than Oc-C1. At C1-C2, the percentages of motion increase were 23%, 97%, 231% and 349% in flexion, extension, lateral bending and rotation. However, the motion increase at Oc-C1 was also significant, especially in extension with 196% increase than normal model. Odontoidectomy with preservation of anterior C1 arch preserved the motion of axial rotation at C1-C2, but the deviant increase also could be seen in extension at Oc-C1（167%） and bending at C1-C2 (181%).ConclusionsOdontoidectomy can produce more motion increase at C1-C2 than Oc-C1，but also produce significant motion increase at Oc-C1. Odontoidectomy with preservation of anterior C1 arch can preserve the axial rotation motion at C1-C2, but the abnormal increase can also be seen in other segmental motions.