Objective To investigate the influence of basic condition, surgical strategy, and postoperative condition of adolescent idiopathic scoliosis (AIS) patients on the length of hospitalization. Methods A total of 145 AIS patients who underwent posterior spinal fusion and internal fixation in The First Affiliated Hospital of Naval Medical University (Second Military Medical University) from Jan. 1, 2014 to Dec. 31, 2023 with more than 2 years of follow-up were retrospectively enrolled. According to the surgical strategy, they were assigned to selective fusion group (n＝50) and non-selective fusion group (n＝95). AIS patients were assigned to intensive care unit (ICU) group (n＝81) and non-ICU group (n＝64) according to whether they were admitted to ICU. Parameters related to basic, surgical and postoperative conditions, hospital stay and postoperative hospital stay were analyzed. Multiple linear regression analysis was used to study the influencing factors of hospital stay and postoperative hospital stay. Results The number of surgical segments, surgical time, intraoperative blood loss, drainage volume on the 3^rd day postoperatively, hospital stay, and postoperative hospital stay in the selective fusion group were significantly less than those in the non-selective fusion group (all P＜0.05). The patients in the ICU group were younger, had longer surgery time, had more intraoperative blood loss and blood transfusion, and had longer hospital stay and postoperative hospital stay compared with those in the non-ICU group (all P＜0.05). Correlation analysis showed that hospital stay and postoperative hospital stay were both positively correlated with ICU admission (r＝0.179, 0.240; both P＜0.05) and were both negatively correlated with selective fusion (r＝－0.187, －0.242; both P＜0.05). Conclusion The hospital stay and postoperative hospital stay of AIS patients with non-selective fusion in posterior spinal fusion and internal fixation is longer than those of patients with selective fusion. Non-selective fusion and ICU admission may be factors contributing to the prolonged hospital stay and postoperative hospital stay in AIS patients.