Objective To investigate the effect of cervical spinous process fracture with posterior ligamentous complex (PLC) injury on biomechanical stability of the goat cervical spine specimen in vitro, and evaluate the role of posterior structure in maintaining the stability of cervical spine. Methods Twenty-four fresh goat cervical spine C3-6 specimens were randomly and evenly divided into 3 groups: control group (group A), simple cervical spinous process fracture group (group B) and cervical spinous process fracture with PLC injury group (group C). Under loading of 1.5 N·m torque, the range of motion (ROM) in each group was respectively measured under 6 working conditions: flexion, extension, lateral bending and axial rotation, and the ROM differences among 3 groups were compared by using one-way ANOVA analysis. Results Simple cervical spinous process fracture had little effect on the stability of cervical spine and there was no significant difference in ROM between group B and control group (P>0.05) under all working conditions. Compared with control group, the ROM in flexion, extension and axial rotation significantly increased in group C (P<0.05), and no significant ROM difference was found in lateral bending between control group and group C (P>0.05). Conclusions Simple cervical spinous process fracture does not affect the overall stability of cervical spine. Cervical spinous process fracture with PLC injury is more likely to cause cervical instability than simple cervical spinous process fracture, and surgical intervention is required in cervical spinous process fracture with PLC injury.