In this paper, we propose a new method of measuring the acoustic impedance of the lung airway to research disease of respiratory system. Conventionally, the acoustic impedance is measured by Forced Oscillation Technique (FOT). FOT method determines the acoustic impedance by superimposing small external pressure signals on the spontaneous breathing of the person. Measured impedance value includes whole lung airway from the person's lips, but important impedance value is which of peripheral airway in the lung airway test and this value is influenced by the shape of vocal tract. We propose a new method to consider an influence of vocal tract. The airway is approximated the acoustic tube, and we measure impulse response at lips, estimate area of cross section and sound pressure, and calculate impedance at the glottis.