Abstract: Background　Mindfulness-based therapy (MBT), a psychological intervention integrating cognitive-behavioral technique, is widely applied in clinical settings. However, systematic validation of its heterogeneous efficacy in alleviating anxiety and depressive symptoms among patients with diagnosed mental disorders remains insufficient. Objective　To systematically evaluate the intervention effects of MBT on anxiety and depressive symptoms in clinically diagnosed mental disorder patients, identify sources of heterogeneity, explore the impact of cultural adaptability on efficacy, and provide evidence-based recommendations for clinical practice.Methods　Randomized controlled trials (RCTs) assessing the efficacy of mindfulness-based therapy (MBT) in improving depressive and anxiety symptoms in patients with mental disorders were included. Twenty-two RCTs (n = 1 723) published from January 2015 to January 2025 were retrieved from PubMed, Web of Science, The Cochrane Library, CNKI, and other English/Chinese databases. A random-effects model was employed for meta-analysis. Heterogeneity was assessed using the Q-test and I² statistics. Subgroup analyses were conducted to investigate heterogeneity sources. Primary outcomes included changes in depressive symptoms (assessed via BDI-Ⅱ, HAMD, or PHQ-9) and anxiety symptoms (assessed via HAMA, BAI, or GAD-7), reported as standardized mean differences (SMD) and 95% confidence intervals (CI).Results　Meta-analysis demonstrated that MBT significantly improved depressive symptoms (SMD = -0.81, 95% CI: -1.13 to -0.49) and anxiety symptoms (SMD = -1.21, 95% CI: -1.74 to -0.67), with moderate-to-large effect sizes. However, high heterogeneity was observed (depression: I² = 89%; anxiety: I² = 93%). Subgroup analyses revealed greater sensitivity of BDI- Ⅱ and PHQ-9 compared to HAMD for depressive symptom assessment (P ＜ 0.01), superior depressive symptom improvement in Eastern cultural contexts versus Western settings (SMD: -1.23 vs -0.42), and enhanced efficacy of short-term interventions (＜8 weeks) over long-term protocols (SMD: -1.63 vs -0.22). Anxiety symptom improvement exhibited scale dependency (highest effect size for GAD-7) and cultural variations. Conclusion　MBT demonstrates robust efficacy in alleviating anxiety and depressive symptoms in mental disorder patients. However, culturally adaptive intervention designs and strategies for sustaining long-term therapeutic benefits require prioritized attention, which provides evidence-based support for personalized clinical interventions.