Objective:To identify the potential impact of cervical spine kyphosis on muscle parameters, the correlation between life quality score and muscle parameters, the correlation between cervical sagittal parameters and muscle parameters.Methods:From September 30, 2019 to September 30, 2020, 30 patients diagnosed with cervical kyphosis and 34 volunteers with normal cervical curvature were enrolled in this case control study. Kyphosis group and control group were matched with sex (χ 2=0.23, P=0.75), age ( t=0.13, P=0.73), BMI ( t=0.26, P=0.20) and neck pain duration time ( t=4.67, P=0.68). Visual analogue scale (VAS) and the neck disability index (NDI) were applied. Cervical sagittal parameters and cervical range of motion (ROM) were measured on lateral radiographs of cervical spine, which included C 2-C 7 lordosis (CL), cervical sagittal vertical axis (C 2-C 7 SVA), T 1-slope (T 1S) and spinal canal angle (SCA). To evaluate muscle functions, Co-contraction ratio (CCR) was measured by surface electromyography (SEMG). Spearman method was used to analyze the correlation between life quality score, cervical sagittal parameters and CCR. Results:VAS in control group 1.4±0.9 was lower than that in kyphosis group (2.3±0.7), and therewasno statistically significant difference ( t=3.71, P=0.30). NDI in control group (4.3%±2.5%) was significantly lower than that in kyphosis group (5.8%±1.7%), and the difference was statistically significant ( t=2.60, P=0.04). CL in control group (-18.76°±2.43°) was significantly lower than that in kyphosis group (13.80°±7.59°) ( t=3.43, P<0.01). SCA in control group (85.94°±4.52°) was significantly higher than that in kyphosis group (84.07°±10.44°) ( t=0.95, P<0.01). T 1S in control group (24.00°±2.85°) was significantly higher than that of kyphosis group (15.47°±11.33°) ( t=4.25, P<0.01), and C 2-C 7 SVA of control group (30.35±6.59 mm) was significantly higher than that in kyphosis group (19.08±14.47 mm) ( t=4.09, P<0.01). ROM in control group (50.23°±3.07°) was significantly higher than that in kyphosis group (45.63°±11.73°) ( t=2.21, P<0.01). CCR from neutral to flexion movement (CCRNF) was significantly lower in control group (0.46±0.20) than kyphosis group (0.84±0.13)( t=12.61, P=0.005), CCR from extension to neutral movement (CCREN) was significantly lower in control group (0.55±0.21) than in kyphosis group (0.79±0.16) ( t=7.10, P=0.042). CCRNF was significantly correlated with VAS ( r=0.504), NDI ( r=0.322), CL ( r=-0.240), T 1S ( r=-0.591), C 2-C 7 SVA ( r=-0.474) and ROM ( r=-0.303, P<0.05). There were significant correlations between CCREN and VAS ( r=0.339), NDI ( r=0.243), CL ( r=-0.347), T 1S ( r=-0.341), C 2-C 7 SVA ( r=-0.346) and ROM ( r=-0.065) ( P<0.05). However, there was no significant difference between CCR and SCA ( P>0.05). Conclusion:SEMG canbe an objective tool to evaluate the degree of neck pain and neck disability index. During cervical flexion movement, patients with cervical kyphosis had more tensional cervical extensor muscle and worse muscle function.