Background: Evidence supports the effectiveness and safety of open-source automated insulin delivery (AID) in patients with type 1 diabetes. However, evidence regarding the clinical application of open-source AID in perioperative patients with type 2 diabetes remains limited. Methods: This was an open-label, single-center, exploratory pilot randomized controlled trial (RCT) with parallel groups. Patients with diabetes (excluding type 1 diabetes mellitus) scheduled for elective surgery were randomly assigned to the closed-loop group (open-source hybrid closed-loop AID system) or the control group (conventional insulin pump). The primary outcome was the percentage of time in the target glucose range (TIR, 3.9–10.0 mmol/L). Other efficacy and safety outcomes were also compared between the groups. Results: A total of 49 participants were included and randomized to the closed-loop group (n = 25) or the control group (n = 24). Participants underwent abdominal, orthopedic, thoracic surgery, or neurosurgery during hospitalization. Patients in the closed-loop group had significantly higher TIR than patients in the control group (76.4 ± 14.1% vs. 61.2 ± 20.0%, p = 0.005). Compared with the control group, the closed-loop group also exhibited a 15.6 percentage point reduction in time above range (TAR, >10 mmol/L) without increasing time below range (TBR, <3.9 mmol/L). There were no episodes of severe hypoglycemia (<2.2 mmol/L) or diabetic ketoacidosis in either group. Conclusions: This study demonstrates that in patients with diabetes undergoing elective surgery, the open-source hybrid closed-loop AID system provides better glycemic control than conventional insulin pump therapy.