The optical waveguide mode convertor and the prepare method for the single mode-multimode or the multimode-single mode is to use the light-sensitive organic resin to form the optical waveguide in the condition of ultraviolet exposal. The method is to couple the single mode waveguide and the multimode waveguide in the free room; the light-sensitive organic resin is added into the coupling end; the resin is solidified by the ultraviolet transferring by the single mode waveguide and the multimode waveguide to form the solid core and the liquid envelope structure of the mode conversion parts; the no solidified light-sensitive organic resin is dissolved and added into another light-sensitive organic resin; the ultraviolet explores in the side of the coupling end to form the solid envelope. The invention has the low cost, so it can be used in the integrated optics, the optical interlinking, the light net and the optical fiber. |