The invention discloses a high-speed electro-optical modulator, which comprises a micro nano optical fiber coupler, a high polymer electro-optic material layer and a plate electrode, wherein the micro nano optical fiber coupler is prepared by intertwining two single mode optical fibers and drawing into a fiber drawing platform, the high polymer electro-optic material layer is coated on the micro nano optical fiber coupler, and the plate electrode is butted against the outside of the high polymer electro-optic material layer. The preparation method of the novel high-speed electro-optical modulator, disclosed by the invention, can efficiently and rapidly prepare an electro-optical modulator with rapid modulation, less optical signal loss, high signal-to-noise ratio and low cost. When the laser from a semiconductor laser is injected into the device from the input end of the electro-optical modulator, and the electrode applies an electrical signal to the two ends of the plate electrode, the unit surface refractive index is changed, resulting in change in synchronous resonant wavelength, which affects the change of the output port optical power, and ultimately an optical signal with the consistent change with the electrical signal is obtained. The high-speed electro-optical modulator disclosed by the invention can be used in the field of optical communication, and the problems of the common electro-optical modulator in the prior art are solved, including high cost, slow modulation and low signal-to-noise ratio.