Abstract: This article presents our research works on interferometric fiber optic sensors for measurements of multi-parameters. Based on a FabryPerot cavity formed by the interfaces between a fiber end and a sensing film or air-gap and between a sensing film or air-gap and the measured object, F-P interference-based and Fresnel-reflection modulated with F-P cavity fiber-optic sensors for temperature measurement and refractive index measurements of liquid and solid have been respectively developed. It is shown theoretically and experimentally that, temperature variation sensing can be converted into the measurement of temperature-dependent peak or dip shift of the interference spectrum, and the fringe contrast of the interference spectrum can be used to determine the RI of liquid or solid. Other functions and applications of an interferometric fiber optic sensor could be extended easily, which is an important development direction in sensing equipment.