1. Introduction
Both the morbidity and mortality of respiratory diseases in children occupy the first place among all systemic diseases in pediatrics. Lung function is an important respiratory physiological index of the human body, which is closely related to the evaluation of children’s growth, development, and motor ability of respiratory diseases, and plays an important role in the diagnosis and efficacy evaluation of respiratory diseases. The measurement of respiratory function has a key role in diagnosing and monitoring respiratory diseases. However, lung function testing is limited in the preschool population because of the poor performance and lack of cooperation by children. The impulse oscillometry system (IOS) is a simple and noninvasive technique for measuring lung mechanics during tidal breathing. It requires no special cooperation from patients and features simple, non-invasive, repeatable, and comprehensive analysis. It can provide a variety of respiratory physiological parameters and is suitable for people aged 3 years and above, especially the elderly and children. How to accurately assess the outcome of lung function is related to the diagnosis and treatment of the disease by clinicians. American Thoracic Society (ATS) and the European Respiratory Society (ERS) are made clear, pulmonary function should be evaluated using the reference from the same ethnicity, living environment and age, and estimated value according to the improper can lead to differences of lung disease assessment results[1,2]. Children’s lung function testing at present in China using the reference from the foreign children, due to differences in race, and so obviously affected the accuracy of the assessment. Therefore, Shanghai Children’s Medical Center was taken as the lead unit, and the pediatrics department of twenty specialized or general hospitals in China were combined to conduct the measurement of IOS lung function in 6284 healthy children from May 2017 to May 2019, aiming to establish the normal reference value of IOS in China, to facilitate the clinical application and research of IOS.