The invention provides a method for enzymatically synthesizing astragalin. The method comprises the following steps that 1, key enzymes needed in the synthesizing process of astragalin are cloned, expressed and purified, wherein the key enzymes comprise glycogen phosphorylase GP, glucose pyrophosphorylase GalU, flavanone-3-hydroxylase F3H, flavanone synthase FLS1 and flavonoid3-O-glucanotransferase UGT78K2; 2, glycogen Gn is synthesized into glucose-1-phosphoric acid G-1-P under the GP effect; 3, G-1-P is synthesized into uridine diphosphate UDPG under the GalU effect; 4, naringenin NRN is synthesized into dihydro kaempferol DHK under the F3H effect; 5, DHK is synthesized into kaempferol KMF under the FLS1 effect; 6, KMF and UDPG are synthesized into astragalin under the UGT78K2 effect. According to the method, few steps are adopted, the operation condition is mild, few side products are generated, the yield is large, pollution is avoided, and the production cost is remarkably reduced.