Taken Pd(0)-catalyzed one-pot cascade reaction as key step, the key intermediate of Amorfrutin B, (E) - 7- hydroxy - 2, 2 - dimethyl - 8 - (3, 7 - dimethylocta - 2, 6 - dienyl) - 5 - phenethyl - 4H - benzo [d] [1, 3] dioxin - 4 – one (Ⅹ) was synthesized efficiently, starting from Meldrum's acid and geraniol within five steps. The structures of all intermediates and final compound were characterized by FTIR and 1HNMR. The reaction conditions of intermediates (E) - 3 - (3,7- dimethylocta- 2, 6- dienyloxy)- 3 - oxopropanoic acid (Ⅲ), and (E)- 3, 7- dimethylocta- 2, 6- dienyl- 4 -(2, 2- dimethyl- 6 - oxo - 6H-1, 3- dioxin- 4 - yl)-3- oxobutanoate (Ⅵ) were also optimized to increase yields and lower down expenses, so as to form a more practical synthetic process. The mechanism of key cascade reaction was explained as that the intermediates (E) - 3, 7- dimethylocta- 2, 6- dienyl 2- (2- (2, 2- dimethyl- 6 - oxo- 6H- 1, 3- dioxin- 4 - yl) acetyl) - 3 - oxo- 5 - phenylpentanoate (Ⅸ) underwent tandem Carroll rearrangement twice, decarboxylation, intramolecular Aldol condensation and final dehydration followed by aromatization to generate key intermediate Ⅹ in one pot. The success of Ⅹ synthesis is believed to play an important role in the total synthesis of Amorfrutin B.