The invention belongs to the technical field of micro sodium manufacturing and discloses a flexible transparent carbon electrode preparation method based on optical diffraction. The method comprises the steps that (1) a substrate is provided, and a negative photoresist is spin-coated on the substrate; (2) a mask is arranged on the photoresist; exposure is carried out; a grid pattern is arranged onthe mask; the grid pattern is rectangular, and four corners thereof are connected with a large-size pattern respectively; (3) a sample after exposure is developed by a developer, and then is cleanedto acquire a photoresist suspension grid; and (4) the sample acquired in the step (3) is pyrolyzed under a protective gas atmosphere, and then is stripped to acquire an independent full carbon grid structure, namely a flexible transparent carbon electrode. According to the invention, the photoresist suspension grid is acquired through single exposure, and the method has the advantages of simple process, easy parameter control and high yield.