A new-style fiber audio transmission method that can be used in the long distance transmission is presented,which performs signal modulation by the strain-optic effects and signal demodulation by the all-fiber interferometer. Both the principles of the audio trans- mission and the capabilities of secure communication are studied. Through the experiments of the sinusoidal signals in the frequency range of 300-3400 Hz and the audio signals,the system shows good capabilities, robust security and maintains audio integrity. The system is applicable in the field of point to point security communication of 40 km long transmission range.