The invention specifically relates to a preparation method of a vanillin ratiometric electrochemical aptasensor based on aptamer/gold nanoparticle/ ferrocene/ Ketjenblack/ZIF-8 nano-composite modifiedelectrode. The method comprises the following steps: dispensing a ferrocene and Ketjenblack doped ZIF-8 nano-composite on the surface of a bare glassy carbon electrode, immersing the modified electrode in a chloroauric acid solution, adopting cyclic voltammetry scanning to electrically deposit gold nanoparticles, and preparing the gold nanoparticles-deposited ZIF-8 nano-composite; connecting a vanillin aptamer to the gold nanoparticles through an Au-S bond, and constructing an aptamer-coupled nano-composite sensing platform; and measuring an electrochemical curve under different vanillin concentrations, fitting a linear relationship between the current peak intensity ratio of the vanillin and the ferrocene and the vanillin concentration, and constructing the vanillin ratiometric electrochemical aptasensor. Compared with the prior art, the method is simple to operate, low in cost, good in ratio signal stability and high in sensitivity, and can be used as a novel ratiometric electrochemical aptasensor for the efficient detection of the vanillin.