Abstract: 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.