Commonly used in Interferometric fiber optic sensor signal demodulating methods: passive homodyne method, phase tracking method, heterodyne method and the heterodyne method and so on. Based on the principle of phase generated carrier demodulation techniques for error analysis, Research proposed an improved carrier phase demodulation method and established a complete relatively interferometric fiber-optic sensing system. Experiments demonstrated that it improved amplitude-frequency characteristics of the original system, and obtained higher detection sensitivity.