Abstract: Objective To investigate the roles of tidal lung function and fractional exhaled nitric oxide(FeNO) detection in bronchiolitis. Methods Children with bronchiolitis who were treated in pediatric department of the hospital from January 2016 to February 2017 were enrolled. The 69 children with bronchiolitis were divided into mild group(24 cases), moderate group(26 cases) and severe group(19 cases) according to disease severity at visit time. MasterScreen spirometer produced by German JAEGER company was performed to monitor tidal volume, ratio of time to peak(TPTEF/TE), ratio of volume to peak(VPEF/VE) and respiratory rate in three groups. Sunvou-D100 Nacolon(Wuxi Shangwo Medicine) Nitric Oxide Analyzer was performed to detect FeNO in three groups. The receiver operating characteristic(ROC) curves were performed to analyze value of tidal lung function combined with FeNO for assessing severity of bronchiolitis. Pearson correlation coefficient analysis was performed to analyze relationship between FeNO and tidal lung function in bronchiolitis children. Results There was no significant difference in tidal volume among mild group, moderate group and severe group(all P>0.05). However, TPTEF/TE and VPEF/VE in mild group were significantly larger than those in moderate group and severe group. The above indexes in moderate group were also significantly higher than those in severe group(all P<0.05). The respiratory rate in mild group and moderate group was significantly lower than that in severe group(all P<0.05). There was no significant difference between mild group and moderate group(P>0.05). FeNO in mild, moderate and severe groups was significantly increased in turn(all P<0.05). ROC curve analysis indicated that the area under the ROC curve of TPTEF+VPEF+FeNO combined detection for assessing bronchitis severity was significantly higher than that of any one of the three. FeNO level in bronchitis patients was significantly negatively correlated with their pulmonary function indexes such as TPTEF/TE and VPEF/VE(r=-0.385,-0.314, all P<0.05). Conclusion Tidal lung function combined with FeNO detection can effectively reflect severity of bronchiolitis. The combination detection of the two may be an effective evaluation method for severity of bronchiolitis.