A respiratory function testing system includes an air transforming device, a sound reception device and an operation device. The air transforming device is configured to collect exhaled air for a predetermined period and generate a full-range sound signal according to the collected exhaled air. The full-range sound signal at least contains an ultrasonic signal. The sound reception device is configured to receive and record the full-range sound signal. The operation device is in communication with the sound reception device and is configured to receive and compute the ultrasonic signal contained in the full-range sound signal recorded by the sound reception device to generate a respiratory function parameter. A respiratory function testing method of the respiratory function testing system is also provided.
