Objective To elucidate the relationship between preoperative C7 slope (C7S) and sagittal parameters in anterior cervical discectomy with fusion (ACDF) by imaging. Methods A retrospective analysis of 54 patients (24 males and 30 females) with ACDF for cervical spondylosis between January 2012 and January 2017 was performed. The age ranged from 23 to 71 years (mean, 46.6 years). There were 29 cases of cervical spondylotic radiculopathy and 25 cases of cervical spondylotic myelopathy. The disease duration ranged from 3 to 48 months, with an average of 16.8 months. In the 55 patients, 44 were single-segment ACDF and 10 were double-segment ACDF. Sagittal parameters of cervical spine were measured on cervical X-ray films before operation and at last follow-up, including C2-7 Cobb angle, C2-7 sagittal vertical axis (C2-7 SVA), C7S, and segment Cobb angle (SCobb), and the changes of C2-7 Cobb angle (the difference between the last follow-up and the preoperative angle) were calculated. Pearson correlation was used to analyze the correlation between the parameters before operation and at last follow-up. According to the preoperative median value of C7S (15°), the patients were divided into group A (C7S<15°) and group B (C7S≥15°). The sagittal parameters before and after operation were compared between the two groups. Results All the 54 patients were followed up 6-45 months (mean, 15.5 months). At last follow-up, C7S, C2-7 Cobb angle, C2-7 SVA, and SCobb angle were significantly improved when compared with preoperative values (P<0.05). Correlation analysis showed that the preoperative C7S and SCobb angles were significantly correlated with C2-7 Cobb angle and C2-7 SVA (P<0.05), but there was no significant correlation between C7S and SCobb angle (r=0.049, P=0.724). There was a significant correlation between C7S, C2-7 Cobb angle, and SCobb angle at last follow-up (P<0.05), but there was no significant correlation between C7S and SCobb angles and C2-7 SVA (P>0.05). According to the median value of preoperative C7S, 28 patients in group A had C7S of (11.82±3.60)°, while 26 patients in group B had C7S of (20.77±4.09)°. There was no significant difference in gender and age between the two groups (P>0.05). The preoperative C2-7 Cobb angle and C2-7 SVA in group A were significantly lower than those in group B (P<0.05). There was no significant difference between preoperative SCobb angle and group B (t=0.234, P=0.816). There were no significant differences in C2-7 Cobb angle, C2-7 SVA, and SCobb angle between group A and group B at last follow-up (P>0.05). However, the change of C2-7 Cobb angle in group A was significantly higher than that in group B (t=2.321, P=0.024). Conclusion Preoperative C7S≥15° group has more physiological lordosis before operation, but its postoperative cervical curvature changes less, while ACDF is more conducive to correct the preoperative C7S<15 ° cervical curvature.