The invention discloses a preparation method of 4,4'-biphenol diglycidyl ether. In the preparation method provided by the invention, 4,4'-biphenol and epichlorohydrin are used as raw materials to be synthesized by a two-step method under the effect of a heterogeneous catalyst. The preparation method comprises the following steps: firstly, carrying out a ring-opening etherifying reaction, then carrying out a ring-closing reaction, and in the alkalizing process, separating out water generated in the reaction by a water-separating technique, so that the reaction shifts to the right at equilibrium, and various hydrolysis secondary reactions in the system can be controlled. The product obtained by the technique has high epoxide equivalent and high yield, the technique has simple reaction stepsand is convenient for posttreatment, and experimental results show that the epoxide number is 0.65-0.67, and the melting range is 159.1-160.4 DEG C.