Abstract: From the homomorphic signal processing used to separate sources of lung soundsand transmission path effects of the lung-thorax system from lung sounds signals, We canobtain the sound transfer function of normal lung-thorax system and abnormal lung-thoraxsystem. Experimental results show that. lung-thorax system can be simulated as a sound lowpass filter,thorax system has sound low-pass characteristics,and the sound transfer functionof abnormal lung-thorax system is significantly different from the sound transfer function ofnormal lun——thorax system.