The invention discloses sesquiterpene cyclase, preparation and application thereof, and a synthesis method of 2Z,4E-alpha-ionylideneehane. At first, the amino acid sequence of provided sesquiterpene cyclase BcABA3 is represented by the sequence 2, and a derived polypeptide is also provided. The sesquiterpene cyclase can catalyze farnesyl pyrophosphate cyclization to synthesize 2Z,4E-alpha-ionylideneehane. At the same time, gene sequence that encodes the amino acid sequence of sesquiterpene cyclase is provided. A recombinant protein containing the amino acid sequence is also provided. The invention further provides a method of using the sesquiterpene cyclase, the recombinant protein, and farnesyl pyrophosphate taken as the substrate to synthesize 2Z,4E-alpha-ionylideneehane and abscisic acid. The invention further provides a recombinant expression carrier containing a sesquiterpene cyclase coding gene, a converter, and applications thereof. A synthesis method of 2Z,4E-alpha-ionylideneehane is also provided; according to the synthesis method, farnesyl pyrophosphate is taken as the substrate, and the synthesis is catalyzed by sesquiterpene cyclase or recombinant sesquiterpene cyclase.