Objective: To explore the value of fractional exhaled nitric oxide (FeNO) in the diagnosis and evaluation of children's asthma in acute stage. Methods: A total of 80 children with acute attack of bronchial asthma admitted to our hospital from March 2017 to June 2018 were recorded as acute group (n=80). According to the severity of the disease, children in acute stage were further divided into mild group (n=32) and moderate severe group (n=48). Thirty-five children in non-acute attack of bronchial asthma admitted at the same period were selected as reference and recorded as non-acute group (n=35). FeNO, FEV1% pred, FVC, IL-6 and CRP were measured in all asthmatic children, The correlation between FeNO concentration and FEV1% PRED, FEV1/FVC, IL-6, CRP in acute stage group was analyzed by Pearman method, and the diagnostic efficacy of FeNO in acute stage of childhood asthma was analyzed by receiver operating characteristic (ROC) curve. Results: All the children were tested. The levels of FeNO, IL-6 and CRP in the acute group were higher than those in the non-acute group, FEV1% pred and FEV1/FVC% were significantly lower than those in the non-acute group (P<0.001). There were significant differences in FeNO concentration, FEV1% pred, FEV1/FVC%, IL-6 and CRP between mild group and moderate group (P<0.001). Spearman linear correlation analysis showed that FeNO concentration was negatively correlated with FEV1% pred and FEV1/FVC%, and positively correlated with IL-6 and CRP. ROC curve suggested that the best cut-off point of FeNO in the diagnosis of asthma in children with acute attack was 39.84 ppb, with sensitivity and specificity of 82.36% and 88.74%. Conclusion: There is a good correlation between FeNO concentration and pulmonary function and inflammatory level in children with acute attack of asthma. Strengthening the monitoring of FeNO is helpful for the early diagnosis and assessment of the degree of disease in the acute stage, and has a certain reference value for guiding the initial treatment.