This time-stratified case-crossover study examined the association between short-term air pollution exposure and childhood asthma hospitalizations in 12 major cities. Analyzing 45,832 hospitalization records from 2018-2022, we found significant exposure-response relationships for PM2.5, NO2, and O3. The strongest associations were observed for NO2, with a 2.8% increase in asthma hospitalizations per 10 μg/m³ increase. Children under 5 years and those from low-income neighborhoods showed heightened susceptibility. These findings underscore the need for stricter air quality standards and targeted protection for vulnerable pediatric populations.