The present invention relates to a method for fabricating a crystal fiber having different regions of polarization inversion, comprising the following steps: (a) providing a source material; (b) putting the source material into a fabricating apparatus; and (c) forming the crystal fiber from the source material, and applying an external electric field on the grown crystal fiber during the growth procedure of the crystal fiber so as to induce micro-swing of the crystal fiber for polarization inversion, whereby poling at the time a ferroelectric crystalline body is being formed, whereas the conventional methods are designed for poling a ferroelectric crystalline body after it has been formed.