【Abstract】 Objective To investigate the influence of FENO on sub acute cough treated by ICS and then observe the value of it on diagnose and treatment of sub acute cough. Methods 200 patients with sub acute cough in our hospital from March 2015 to October 2015 were divided into PIC group, CVA group, EB group, UACS group, GERC group and double causes group. The cough degree, FENO, pulmonary ventilation function and treatment response were observed. Results FENO level of PIC group ［12（732）ppb］ was lower than that of CVA group ［205（1332）ppb（Z=-3385，P＜001）］ and EB group ［ 22（1235）ppb（Z=-3372，P＜001）］. FENO level of PIC group was higher than that of UACS group ［7（69）ppb（Z=-3011，P＜001）］, GERC group ［35（34）ppb（Z=-2115，P＜005）］ and double causes group ［7（69）ppb（Z=-2336，P＜001）］. FENO level of CVA group and EB group had not obvious difference (Z=-0739，P=0341). Compared with that of CVA group, FEV1 of PIC group and EB group were obviously increased (P＜005). MMEF pred% in PIC group （9624±1727）% and EB group （9812±1472）% were obviously higher than that of CVA group （5836±1667）%, P＜001. FVC pred% and FEV1/FVC% had no obvious difference between each group( P＞005). Induced sputum oxyphil cell rate of EB group was lower than that of CVA group. nduced sputum oxyphil cell rate of CVA group and EB group were obviously higher than that of other groups (P＜001). The results showed that, FENO level and suptum eosinophil cell percentage had obvious positive correlation (R=0928，P＜0001). Conclusion Using FENO≥19ppb as a standard can predict reflection of ICS on cough condition. FENO should be supported as important reference index on ICS therapy.