A complete Electrical ImpedanceTomography system that can monitor lung function is introduced in this paper. The master PC is responsible for visual control and image reconstruction, while DSP carries out tasks such as electrode selection, data acquisition and data communication with the master. Based on the DDS technique, the exciting signal source has high accuracy, and the data can be acquired by phase-sensibility demodulation. The vivo experiment proves that gravity exerts an effect on the distribution of intrapulmonary ventilation, and shows that the Electrical ImpedanceTomography is able to monitor lung circulation and check pathological changes.