Abstract： Objective:To explore the related factors affecting the surgical outcome in patients with Chiari malformation type Ⅰ (CM-Ⅰ).Methods:The clinical data of 77 CM-Ⅰ patients admitted to the Department of Neurosurgery of the Second Hospital of Lanzhou University from January 2017 to December 2020 were retrospectively analyzed. Twenty-five cases were treated with posterior cranial fossa bony decompression and expanded dural angioplasty, and 52 cases were treated with posterior approach fixation. The Chicago Chiari outcome scale (CCOS) was used to evaluate the short-term efficacy (at discharge), long-term efficacy (≥3 months after surgery), and the improvement of curative effect(improvement of long-term efficacy over short-term efficacy). The influencing factors of CM-Ⅰ operation efficacy were analyzed by univariate analysis and multiple linear regression model.Results:The CCOS scores at discharge varied in patients with different first symptom( P=0.008). Patients without limb weakness, abnormal sphincter function, cerebellar ataxia, unsteady walking or scoliosis before operation, and those with low national nosocomial infection surveillance risk index(NNIS) scores had higher CCOS scores at discharge, and the differences were statistically significant (all P<0.05). Patients with preoperative occipital pain, American Society of Anesthesiologists (ASA) anesthesia class Ⅰ, and those without platybasia had higher CCOS scores ≥3 months after operation, and the differences were statistically significant (all P<0.05). Patients aged 18 to 40 years old, with preoperative limb weakness, combined with atlantoaxial dislocation, atlanto-occipital fusion, without platybasia and treated with posterior approach fixation had more improvement in terms of the CCOS score, and the differences were statistically significant (all P<0.05). Preoperative limb weakness and scoliosis were the influencing factors of short-term efficacy after CM-Ⅰ surgery (both P<0.05). ASA preoperative anesthesia risk classification was the influencing factor of long-term efficacy after CM-Ⅰ surgery ( P=0.047). Preoperative limb weakness and platybasia were the influencing factors for the improvement of curative effect of CM-Ⅰ (both P<0.05). Conclusions:CM-Ⅰ patients without limb weakness or scoliosis before surgery have better short-term postoperative outcomes. Patients with lower ASA preoperative anesthesia risk classification have better postoperative long-term outcomes. CM-Ⅰ patients with preoperative limb weakness and without platybasia have better improvement of curative effect.