ing at the requirements of oceanic profile observation and problems of traditional expendable bathythermograph(XBT), we propose a kind of optical fiber temperature-depth oceanic profile sensor based on fiber Bragg grating-long period fiber grating (FBG-LPG) cascaded structure (fiber XBT), and design and optimize the optical path by using the reflective optical fiber end mirror. The experimental results show that, when the end reflectivity of fiber is in the range from 48.8% to 72.5%, the resonant peaks of FBG and LPG are reasonable and the whole spectrum is suitable for demodulation.