Background: Asthma is a prevalent chronic respiratory disorder with marked regional management disparities; comprehensive epidemiological research is critical to guide targeted interventions. Methods: This ecological study utilized de-identified aggregate data from the Global Burden of Disease Study (GBD) 2021, covering 204 countries/territories and all age groups (0–95+ years). The Bayesian Age-Period-Cohort (BAPC) model was employed to forecast asthma burden trends from 2022 to 2040, with age-standardized rates and 95% uncertainty intervals (UI) used for statistical analysis. Results: In 2021, 260.5 million global asthma cases were reported (age-standardized prevalence rate [ASPR]: 3,340.1 per 100,000), a 38.7% decrease since 1990 (EAPC: -1.59, 95% CI: -1.74 to -1.43). Low sociodemographic index (SDI) regions saw increased cases (42.9 million) but decreased ASPR, while other regions declined in both. An unbalanced-M shaped association between SDI and age-standardized disability-adjusted life year (DALY) rate was identified (1990–2021, P ? 0.001). By 2030, global cases are projected to reach 292.3 million (95% UI: 201.7–384.9) as a primary benchmark aligned with UN Sustainable Development Goals (SDGs); 2040 estimates are 321.0 million (95% UI: 113.5–528.6), interpreted as a plausible scenario due to long-range uncertainties. Low SDI regions face greater growth, while high SDI regions maintain higher ASPR (3,508.4 per 100,000 by 2040). Conclusions: This study reveals a multifaceted asthma epidemiological pattern marked by declining ASPR and an SDI-linked bimodal DALY burden. While global burden has plateaued, high and low SDI regions require tailored interventions to address distinct challenges, providing evidence for global asthma prevention strategies.