The invention provides a preparation method of 1,1,1,5,5,5-hexafluoro acetylacetone. The preparation method comprises the following steps: carrying out first-stage reaction on trifluoroacetyl acetate and trifluoroacetic anhydride under the action of a catalyst at 40-60 DEG C for 5-10 hours; then raising the temperature to 120-150 DEG C for second-stage reaction, and distilling out the resulting 1,1,1,5,5,5-hexafluoro acetylacetone while reacting to obtain a crude 1,1,1,5,5,5-hexafluoro acetylacetone product; and finally purifying the crude product to obtain a refined 1,1,1,5,5,5-hexafluoro acetylacetone product. In the preparation method provided by the invention, as inexpensive trifluoroacetic anhydride and trifluoroacetyl acetate are used as raw materials for the reaction, the cost of the product is dramatically reduced; and as no acid is generated in the reaction process, the environmental pollution is low.