Objective To investigate the effects of preoperative insomnia on postoperative pain in patients undergoing non‑cardiac surgery. Methods A total of 400 patients who underwent non‑cardiac surgery in Beijing Chaoyang Hospital, Capital Medical University from September 2019 to January 2020 were enrolled and their clinical data were retrospectively analyzed. The Insomnia Severity Index (ISI) was used to evaluate preoperative insomnia, and 43 patients with a score of 8‒14 points were set as a mild insomnia group. Meanwhile, the propensity score was used and 42 patients were set as a control group. Then, their general information, anesthesia information during surgery, the Visual Analogue Scale (VAS) scores 1, 24, 36, 48, 60, 72 h, and 84 h after surgery and postoperative nausea and vomiting were collected. Results Compared with the control group, the mild insomnia group presented significant increased VAS scores 1, 24, 60 h after surgery, and VAS score and ISI score were positively correlated 1 h after surgery (r=0.223, P<0.05) and 24 h after surgery (r=0.342, P<0.05). There was no statistical difference in VAS score between the two groups at other time points (P>0.05). There was no statistical difference in intraoperative medication, postoperative analgesia and rescue analgesia between the two groups (P>0.05). The wild insomnia group showed a remarkably increased incidence of postoperative vomiting (11.6%), compared with the control group (0) (P<0.05). Conclusions Preoperative mild insomnia may aggregate postoperative pain, and VAS score is associated with ISI score..