The invention mainly aims to provide a 1, 10a-dihydro-2H-pyridine [1, 2-d] [1, 4] thiazepine compound and a preparation method thereof. According to the method, the 1, 10a-dihydro-2H-pyridine [1, 2-d][1, 4] thiazepine compound can be efficiently synthesized through reaction of sulfur-containing onium salt and allene at 65 DEG C only under the condition that dichloromethane is used as a solvent without participation of other reagents. The invention also provides a preparation method of the 1, 10a-dihydro-2H-pyridine [1, 2-d] [1, 4] thiazepine compound. Other reaction reagents do not need to beadded, an aza-six-membered ring and seven-membered ring skeleton can be simply constructed and is expected to be applied to synthesis work of drug molecules, reaction raw materials are easy to obtain, reaction operation is simple, other noble metal catalysts do not need to be added, aftertreatment is convenient, substrate applicability is wide, the yield is generally very high, and inert gas protection is not needed in the preparation process. The reaction conditions are mild, the reaction can be quickly and smoothly carried out at 65 DEG C and large-scale preparation is easy.