The invention discloses a method for synthesizing 5,7-dihydroxy flavone. The method comprises the following steps of: acetylating 1,3,5-trimethoxybenzene to generate 2,4,6-trimethoxybenzene ethyl ketone; condensing the 2,4,6-trimethoxybenzene ethyl ketone and methyl benzoate to generate 1-(2'-4'-6')-trimethoxy-3-phenyl-1,3-propanedione; and performing cyclization and demethylation on the 1-(2'-4'-6')-trimethoxy-3-phenyl-1,3-propanedione to prepare the 5,7-dihydroxy flavone so as to obtain chrysin. In the method, the 1,3,5-trimethoxybenzene is directly taken as a starting raw material, a target product is obtained by performing friedel-crafts acylation reaction, ester exchange, cyclization and demethylation, and the cyclization and the demethylation are performed in one step instead of two steps. The method has the advantages of low cost, low environmental pollution, low equipment requirement and mass production.