Objective To investigate the effect of facet joint resection at different ranges under endoscopy on the stability of the cervical spine and provide a biomechanical theoretical basis for clinical surgery. Methods A normal finite element model of The cervical spine C5-6 was established based on CT data, and unilateral facetectomy models with different ranges (0, 25%, 50%, 75%, and 100%) of laminectomy were obtained (Models 1-5) by simulating cervical endoscopic surgery. The ranges of motion (ROMs) of C5-6 and the von Mises stresses of the discs for the models in each group were compared and analyzed. Results Except for flexion, Models 1 and 2 showed insignificant changes in ROMs and disc von Mises stresses in each direction compared with those of the normal model. Model 3 showed a noticeable increase in ROMs and disc von Mises stresses in each direction compared with those of the normal model: ROMs under flexion, extension, left lateral bending, right lateral bending, left rotation, and right rotation increased by 27%, 4%, 3%, 13%, 5%, and 16%, respectively, and von Mises stresses increased by 32%, 4%, 2%, 5%, 9%, and 5%, respectively. Models 4 and 5 exhibited a significant increase in the ROMs and disc von Mises stresses in each direction compared to the normal model. For Model 4, ROMs were increased by 27%, 14%, 6%, 24%, 7%, 167%, and von Mises stress were increased by 33%, 13%, 3%, 32%, 10%, 130%. For Model 5, ROMs were increased by 27%, 17%, 6%, 25%, 7%, 167%, and von Mises stresses were increased by 33%, 29%, 8%, 33%, 12%, 138%. Conclusions As the range of unilateral facetectomy increased, cervical ROM and disc von Mises stress extremum gradually increased. The cervical spine shows a significant ROM increase and stress changes when facet joint resection on one side exceeds 1/2. More than 1/2 of the facet joint should be preserved during surgery to avoid medical instability.