OBJECTIVE: To explore the association between perioperative SARS-CoV-2 infection and the postoperative complications during the breakout of the Omicron epidemic wave. DESIGN: Observational retrospective cohort study. Multivariable logistic regression was performed to explore the association between the duration from surgery to COVID-19 diagnosis and the likelihood of postoperative complications. SETTING: A general hospital in China. PARTICIPANTS: 7927 patients aged 18 years and older who underwent surgical treatment between 1 December 2022 and 28 February 2023. PRIMARY OUTCOME MEASURES: The outcome was a composite of postoperative adverse events that occurred within the initial 30 postoperative days. RESULTS: Of all patients, 420 (11.76%) experienced postoperative complications. Compared with No COVID-19, preoperative COVID-19 within 1 week (pre-1w) exhibited a high risk of postoperative complications (adjusted OR (aOR), 2.67; 95% CI 1.50 to 4.78), followed by patients with pre-2w (aOR, 2.14; 95% CI 1.20 to 3.80). For patients with postoperative COVID-19 within 1 week (post-1w), the aOR was 2.48 (95% CI 1.48 to 4.13), followed by patients with post-2w (aOR 1.95; 95% CI 1.10 to 3.45), and those with post-3w (aOR 2.25; 95% CI 1.27 to 3.98). The risks of postoperative complications decreased roughly with the increase of the time interval between the surgery date and SARS-CoV-2 infection. Stratification analyses suggested that perioperative COVID-19 increased the risk of postoperative complications in older patients, smokers, those with comorbidities or experiencing moderate or severe COVID-19 symptoms. CONCLUSIONS: Our findings reveal a significant time-dependent relationship between perioperative COVID-19 and postoperative complications, highlighting the importance of tailored preoperative risk evaluations, enhanced postoperative surveillance, and the implementation of effective postoperative COVID-19 prevention measures. TRIAL REGISTRATION NUMBER: ChiCTR2300072473.