To assess whether preoperative T1 slope and cervical lordosis mismatching affect the surgical outcomes of patients with cervical spondylotic myelopathy (CSM) after laminoplasty.A total of 85 patients with CSM who underwent unilateral open-door laminoplasty between January 2013 and May 2017 were retrospectively reviewed. Based on preoperative T1 slope and C2-C7 lordosis matching, the patients were divided into 2 groups: the match group and the mismatch group. The T1 slope minus C2-C7 lordosis (T1S-CL) <20° was defined as matching. Radiographic parameters included T1 slope, C2-C7 lordosis, C2-C7 sagittal vertical axis (SVA), and T1S-CL. Clinical outcomes were based on the Neck Disability Index (NDI) and Japanese Orthopedic Association (JOA) scores.The preoperative T1S-CL had significant correlation with T1 slope (r = 0.283), C2-C7 lordosis (r = -0.611), and C2-C7 SVA (r = 0.331). At the final follow-up, patients in the mismatch group had a higher incidence of postoperative cervical kyphosis (P = 0.007) and C2-C7 SVA >40 mm (P = 0.043). The mismatch group also had greater △C2-C7 lordosis (P = 0.028), △C2-C7 SVA (P = 0.042), and △T1S-CL (P = 0.044). Comparison of clinical outcomes revealed that patients in the match group had better NDI and JOA recovery (P < 0.05).T1S-CL is a clinically relevant parameter for surgical decision making because patients with T1S-CL mismatching are more likely to have postoperative kyphotic alignment changes and cervical sagittal imbalance. Laminoplasty might not be a suitable option for patients with T1S-CL mismatching.