Objective To evaluate the effect of preoperative gastric contents and poor glycemic control on residual gastric volume (RGV) in diabetic patients by ultrasound. Methods A total of 225 patients who underwent elective surgery at the Second Hospital of Lanzhou University from March 2022 to June 2023 were selected. According to the blood glucose levels at admission, the patients were divided into three groups (n=75): a good glycemic control group (group A), with fasting blood glucose ≤10.0 mmol/L and glycated hemoglobin (HbA1c) ≤7%; a poor glycemic control group (group B), with fasting blood glucose >10.0 mmol/L and HbA1c >7%; and a non‑diabetic patient group (group C), with fasting blood glucose ≤7.0 mmol/L at admission. Patients in group A continued their original oral hypoglycemic regimen, while those in group B switched to short/rapid‑acting insulin for rapid glucose regulation to ≤10.0 mmol/L within 48 h before surgery. Before anesthesia induction, antral grades (grades 0, 1 and 2), cross‑sectional area (CSA), RGV, and the probability of risk stomach (RGV>1.5 ml/kg) were assessed and compared among the groups by point‑of‑care ultrasound. Results The number of patients with antral grade 2, CSA and RGV were significantly higher in group A and group B than those in group C (all P<0.05). There was no statistical difference in antral grades, CSA and RGV between group A and group B (all P>0.05). The probability of risk stomach, CSA and RGV were significantly higher in group A and group B than those in group C (all P<0.05). The probability of risk stomach, CSA and RGV were higher in group B than those in group A, without statistical difference (all P>0.05). Conclusions Before anesthesia for elective surgery, diabetic patients have significantly larger RGV than non‑diabetic patients, while rapid preoperative glycemic control cannot significantly reduce RGV.