Objective To assess the diagnostic value of the flow velocity gradients of resistance(dR/dV') in treating airway obstruction using impluse oscillometry. Methods The dR/dV' value, FEV 1, V 50, and V 25 were measured and compared using 72 cases including control, smoking and COPD groups. The dR/dV' values were regressed with FEV 1, V 50 and V 25, respectively. Results Significantly different dR/dV' values were found between control and smoking groups and between control and COPD groups, but not between smoking and COPD groups. Significantly negative correlation was found between dR/dV' and FEV 1, and similarly, between dR/dV' and V 50 and between dR/dV' and V 25. If the dR/dV' value exceeded x ±1.65s it was considered abnormal, and the misdiagnosis rate was 4.17% in the normal group, while the positive rate reached 41.67% in 48 cases (smoking and COPD groups). Conclusion The dR/dV' is considered an index for detecting airway obstruction, but is not accurate in reflecting the severity of the disease.