Objective Delirium has been reported in all the course of COVID-19, especially in aged patient with severe SARS-CoV-2 infection, but there are few studies on these millions of patients with none-severe omicron infection. To study the incidence of delirium and its factors in hospitalized elderly patients with non-severe Omicron infection，we reported this single-center observational study. Methods Patients tested positive for SARS-CoV-2 infection at the hospital were included. We used the 3-min diagnostic Confusion Assessment Method for delirium diagnosis. We collected the demographic data, medical history, number of vaccine doses against COVID-19, the first laboratory tests and chest computed tomogram, days to the outcome, and medications to treat COVID-19. Results The data of 311 (131M,180F, aged75±7y) patients were analyzed, of whom 73 ( 29M,44F,  23.47%) patients were diagnosed with delirium. Higher incidence was associated with lager age, lager body mass index, smaller total protein, lower albumin-to-globulin ratio, and higher platelet-large cell ratio. These parameters were used to create a risk prediction model, which showed good predictive accuracy.  Conclusion We found that delirium is frequently seen in elderly patients even with non-severe Omicron infection. Age, body mass index, total protein, albumin-to-globulin ratio, and platelet-large cell ratio were identified as independent factors for delirium. Our findings may be useful to physicians in early prevention and treatment of delirium.