The invention discloses an automatic lung function measuring instrument. The automatic lung function measuring instrument comprises a shell, a display screen, an airflow pipe and a control circuit, wherein the display screen is arranged on the outer side of the shell, and the airflow pipe and the control circuit are packaged inside the shell; the control circuit comprises a microcontroller, a power supply, ultrasonic sensors, a storage chip and a wireless communication module, the display screen, the power supply, the ultrasonic sensors, the storage chip and the wireless communication module are electrically connected with the microcontroller, and the ultrasonic sensors are arranged at the two ends of the airflow pipe. The invention also discloses a lung function measuring method based onthe automatic lung function measuring instrument. According to the automatic lung function measuring instrument and the lung function measuring method, by introducing the sensors, accurate measurementof lung capacity information is achieved, the effects of being small and convenient, easy to operate and high in measurement accuracy are achieved, and the automatic lung function measuring instrument and the lung function measuring method are suitable for a person and a family to use; meanwhile, the lung capacity information is processed and classified, professional medical workers can conveniently analyze the information, doctors accurately judge conditions remotely, users understand body conditions, and the automatic lung function measuring instrument and the lung function measuring methodare suitable for a person and a family to use.