The invention discloses preparation of a corundum fiber insulating paper for transformers. The corundum fiber insulating paper for transformers is prepared from the following raw materials by weight part: 12-15 of nano-titanium dioxide, 2-3 of phenolic resin, 500-550 of a pulp board, 1.3-1.5 of sodium silicate, 1-1.3 of sodium carboxymethyl cellulose, 2.3-2.6 of corundum fiber, 0.5-0.6 of ammonium polyphosphate, 0.8-0.9 of urea, 0.6-0.8 of hydroxymethyl starch, 0.2-0.4 of polyethylene oxide, and a proper amount of deionized water. The preparation method provided by the invention is simple, the raw materials are low in cost and have wide sources, the prepared insulating paper has good performance and high stability, and has good use prospect as an insulating part of transformers.