Background：Asthma control level is much lower in children. This study aimed to determine the role of small airway function in predicting asthma control in preschool children. Method: In this retrospective cohort study, we enrolled preschool children who initially diagnosed with asthma and followed up 2 to 3 months by pediatric pulmonary physicians. Clinical history and lung function results were collected. Multivariable regression model was applied to determine risk factors in predicting poor asthma control. Results: The cohort study was comprised of 219 preschool children. Sixty-nine of them (31.5%) had poor asthma control. Poor adherence (14.5% vs 6.0%, p=0.038) and severe airway hyperresponsiveness (AHR) (20.6% vs 1.6%, p＜0.05) were more common in poor controlled group. Baseline FEV ₁% (94.5 vs 101.4, p=0.001), FEF50% (66.1 vs 86.0, p＜0.001), FEF75% (60.9 vs 75.3, p=0.001), FEF25-75% (70.9 vs 86.0, p＜0.001) were significantly lower in poor controlled patients than those of well controlled group. While, FVC% was similar between the two groups (92.4 vs 96.7, p=0.093). Multivariable regression models showed severe AHR (OR 9.500, 95%CI 1.404-64.000, p=0.020), lower baseline FEF50% (OR 0.972, 95%CI 0.950-0.994, p=0.012) were significantly associated with short-term poor asthma control (AUC, 0.740, 95%CI 0.661-0.818). Conclusion: Preschool asthma children with severe AHR and decreased FEF50 were at risk of poor asthma control in next 2 to 3 months.