We examined the relationship between RAAS inhibitor use and Omicron infection in mildly symptomatic patients. This retrospective case-control observational study included 50,121 patients with mild Omicron infection from the largest "Fangcang" shelter hospital in Shanghai between April 9, 2022, and May 21, 2022. Using 1:1 propensity score matching (PSM), we classified 4394 COVID-19 patients into hypertension and non-hypertension groups, and 406 hypertensive patients into RAAS inhibitor and non-RAAS inhibitor groups. The risk of initial symptoms of infection, cumulative negative conversion rates, time to nucleic-acid negative conversion, and viral loads were compared. In the hypertension group, the median number of days for nucleic-acid negative conversion was 7.0 (IQR, 5.0-9.0), which was greater than non-hypertensive group (median (IQR) 6.0 (4.0-8.0), P < 0.001, Cohen's d = 0.29); the mean and minimum cycle threshold values (CT-values) were significantly lower (P < 0.001, Cohen's d = 0.23). In the RAAS inhibitors group, the median number of days for nucleic-acid negative conversion was 7.0 days (IQR, 5.0-9.0), which was shorter than the non-RAAS inhibitors group ([median (IQR)] 8.0 (6.0-10.0), P < 0.001, Cohen's d = 0.34), the cumulative negative conversion rates at 3-8 days being all higher than non-RAAS inhibitors groups (P < 0.05). The most significant difference in negative conversion rate between the RAAS inhibitor and non-RAAS inhibitor group was on the 4th day. No significant difference was observed in mean and minimum CT-values from RAAS inhibitor and non-RAAS inhibitor groups (P > 0.05). RAAS inhibitor use in patients with hypertension is associated with nucleic-acid negative conversion duration and negative conversion rate. RAAS inhibitors clearly do not aggravate or prolong COVID-19.