Objective To analyze the effect of different opioid analgesics on postoperative pain after cesarean section. Methods A total of 332 patients who were admitted to the Obstetrics and Gynecology Hospital of Capital Medical University from June to September 2022 and met the inclusion/exclusion criteria were enrolled for retrospective analysis. Their general information, comorbidity, clinical medication and postoperative analgesia follow‑up records were collected. Then, univariate and multiple linear regression analyses were conducted for correlative analysis of postoperative Visual Analogue Scale (VAS) scores. Results The results of univariate analysis showed that when the dose of morphine was considered as a categorical variable, patients who received 2.0 mg of morphine showed significant decreases in VAS scores compared with those without morphine administration [odds ratio (OR) −0.8 (95% confidence interval (CI) −1.3, −0.2), P=0.009]. According to the doses of epidural morphine through continuous variable analysis, the postoperative VAS scores exhibited a decreasing trend with the increase of morphine dose [β −0.4 (95%CI −0.7, −0.1), P=0.011]. Multiple linear regression results indicated that, after adjustment of variables such as height, weight, age, patient‑controlled epidural analgesia (PCEA) pump, pregnancy with hypertension and diabetes, water fasting in the morning, intraoperative bleeding and fluid rehydration, single epidural administration of morphine was still negatively correlated with VAS scores, when the dose of morphine was considered as a continuous variable [β −0.5 (95%CI −0.9, −0.2), P=0.003] and a categorical variable [OR −1.0 (95%CI −1.7, −0.4), P=0.002]. Conclusion Single epidural administration of 2.0 mg morphine may be an independent factor for the reduction of VAS score after cesarean section.