The impact of the COVID-19 pandemic on clinically stable older patients with psychiatric disorders is unclear. This study examined the prevalence of depressive and anxiety symptoms, and their associations with quality of life (QOL) in clinically stable older patients with psychiatric disorders during the COVID-19 pandemic. This was a multicenter, cross-sectional study. Depressive and anxiety symptoms, insomnia, pain, and QOL were assessed with standardized instruments. A total of 1063 patients were included. The prevalence of depressive and anxiety symptoms, and combined depressive and anxiety symptoms were 62.3% (95%CI = 59.4–65.2%), 52.4% (95%CI = 49.3–55.4%), and 45.9% (95%CI = 42.9–48.9%), respectively. Patients with depressive and anxiety symptoms had significantly lower QOL than those without (P < 0.01). Binary logistic regression analyses revealed that having depressive symptoms was positively associated with more severe insomnia (OR = 1.29, P < 0.01) and pain (OR = 1.14, P < 0.01), and was negatively associated with other psychiatric diagnoses (except for major depressive disorder, schizophrenia, and organic mental disorder; OR = 0.50, P < 0.01), while having anxiety symptoms was positively associated with severe physical diseases (OR = 1.57, P = 0.02), poor adherence to treatment (OR = 1.50, P < 0.01), and more severe insomnia (OR = 1.15, P < 0.01) and pain (OR = 1.11, P < 0.01). Having combined depression and anxiety symptoms was positively associated with poor adherence to treatment (OR = 1.42, P = 0.02) and more severe insomnia (OR = 1.19, P < 0.01) and pain (OR = 1.15, P < 0.01), and was negatively associated with the diagnosis of schizophrenia (OR = 0.50, P = 0.04) and others (OR = 0.53, P < 0.01). Depressive and anxiety symptoms were common in clinically stable older patients with psychiatric disorders during the COVID-19 pandemic. Considering the negative impact of these symptoms on QOL, regular screening and appropriate treatment are recommended for this population.