Abstract: Flavaspidic acid AB is a bicyclic phloroglucinol derivative with various biological activities in Dryopteris fragrans (L.) Schott. The structure of flavaspidic acid AB was analyzed by inverse synthesis techniques, and its synthesis was designed under the principle of association. Using phloroglucinol as raw material, the 2-methyl-4-butyrylphloroglucinol was synthesized by Vilsmeier-Haack reaction, reduction and acylation, and the flavaspidic acid fragment was synthesized by acylation, alkylation and deacylation, after which N, N-dimethylmethyleneammonium iodide was activated and the flavaspidic acid AB was obtained. The structures of intermediates and flavaspidic acid AB were confirmed by MS, ¹H NMR and ¹³C NMR, and the yield of the target product reached 14.7%. Results indicate that the designed synthetic route of flavaspidic acid AB is simple and easy.