The invention discloses a tunable long period fiber grating structure and fabrication method, which produces an expected microbending deformation by adjusting the temperature and making use of the unmatched coefficients of thermal expansion between different materials, and thus creating a phenomenon of mode coupling effect occurred in traditional optical gratings in order to provide the structure and fabrication method for having an effect of tuning spectra by controlling the temperature. This invention not only can be applied to the optical communications and wavelength dependent multiplexed devices and equipments, but also can be applied to the temperature and deformation detection. The tunable long period fiber grating structure in accordance to the present invention comprises a substrate; a periodic structure being disposed thereon and having a first coefficient of thermal expansion; a coupling agent, having a second coefficient of thermal expansion for fixing a fiber to the periodic structure; wherein the first and second coefficients of thermal expansion are different.