A 4-year-old boy with no significant medical history was transferred to the pediatric intensive care unit of Henan Provincial People´s Hospital on April 10, 2022. His chief complaints were fever, drowsiness for 5 days, cough for 2 days, dyspnea for 1 day and 5 h after extracorporeal membrane oxygenation (ECMO). Two days before admission, the child came to the local hospital, where he was considered to have community-acquired pneumonia and received antibiotics and aerosol therapy. One day before admission, the child developed dyspnea and hypoxemia, and was transferred to Zhumadian Central Hospital for endotracheal intubation and ventilator assisted breathing. On April 10, alveolar lavage fluid and peripheral blood samples were taken for metagenomics next-generation sequencing(mNGS). Chest CT showed pneumonia in the upper and lower lobe of the right lung and left lung (Fig. 2A). After 1 day of treatment with antibiotics and "oseltamivir", the fluctuation of blood oxygen saturation under high ventilator parameters was 60–80%, and the oxygenation index was 50. ECMO was recommended. With the consent of the children´s parents, the ECMO team of our hospital rushed to the local hospital for femoral vein-internal jugular vein ECMO catheterization 5 h before admission to our hospital. The mNGS results of the bronchoalveolar lavage fluid and peripheral blood samples collected on April 10 showed that 7,888,701 reads suspected H3N8 viruses were detected in the bronchoalveolar lavage fluid and 192 reads in the blood. After admission, patients were given ECMO combined with ventilator for assisted respiration,"oseltamivir" for antiviral, "meropenem" for anti-infection, "methylprednisolone sodium succinate" to reduce inflammation, "plasma and immunoglobulin" infused and other treatments. On April 12, bronchoalveolar lavage was performed again. The mNGS re-examination showed 183 reads virus sequences in the bronchoalveolar lavage fluid, and no virus sequences was detected in the blood. Part of bronchoalveolar lavage fluid sample was sent to the Center for Disease Control and Prevention. Whole genome sequencing confirmed the positive for avian H3N8 influenza virus, and H3N8 influenza virus was successfully isolated from the bronchoalveolar lavage fluid. On April 19, chest CT showed extensive interstitial changes and consolidation in the lungs, with obvious small airway involvement(Fig. 2B). Multiple deep lavage was performed with bronchoscope with an outer diameter of 2.8 mm. On April 20, the number of virus sequences in the bronchoalveolar lavage fluid decreased to 10 reads, and no virus was detected in peripheral blood. The child is in critical condition and is still receiving ECMO combined with ventilator support so far.