[Objective] To analyze the changes of neck extensor muscle (NEM) and cervical sagittal parameters secondary to posterior unilateral open- door laminoplasty, and to explore the correlation between postoperative NEM atrophy and cervical sagittal parameters. [Methods] A total of 128 patients underwent posterior cervical unilateral open-door laminoplasty in our hospital from January 2015 to July 2019. Imaging examinations were performed before surgery, 1 week after surgery, 1 year after surgery and 2 years after surgery to measure the C2~7 Cobb angle, C2~7 SVA and T1S, additionally the SEA/VBA and DEA/VBA, which presented the abundance of NEM, as well as the fat content of the NEM. Correlation analysis was conducted between the sagittal plan parameters and the NEM measurements. [Results] The C2~7 SVA, C2~7 Cobb angle, T1S, as well as SEA/VBA, DEA/VBA and NEM fat content had curve variations over time, which were statistical- ly significant among time points (P＜0.05) . As consequences of Spearman analysis, the SEA/VBA and DEA/VBA were significantly positive- ly correlated with C2~7 Cobb angle and C2-7 SVA (P＜0.05) , whereas the NEM fat content was significantly negatively correlated with the C2~7 Cobb angle (P＜0.05) , and the fat content of C7/T1 NEM was positively correlated with T1S (P＜0.05) . [Conclusion] The cervical spine pres- ents a trend of lordosis after posterior unilateral open-door laminoplasty, and NEM atrophy is correlated with the changes of cervical sagit- tal parameters.