The invention discloses a benzopyrrolizidine alkaloid, and a preparation method and application thereof, belonging to the fields of preparation technology of chemical pharmacy and fine chemical engineering. According to the invention, polysubstituted and multifunctional one-pot synthesis of 9-amino-9a-allyl benzopyrrolizidine alkaloid is realized; metal-catalyzed sulfonyl triazole is decomposed into metal carbene, then metal carbene undergoes cyclization and rearrangement, and then Lewis acid is further utilized to catalyze electrophilic cyclization, so the 9-amino-9a-allyl benzopyrrolizidine alkaloid with a high added value is highly efficiently obtained. The preparation method provides a first technical route for high-efficiency preparation of functionalized 9-amino-9a-allyl benzopyrrolizidine alkaloid derivatives and has a wide application scope in the fields of chemical pharmacy and fine chemical engineering. Latent biological activity of the 9-amino-9a-allyl benzopyrrolizidine alkaloid is proved in the invention.