In this paper, methyl bromoacetate and triphenylphosphine were used as starting materials. First, bromophosphorus salt was prepared, and then alkali was added to prepare Wittig reagent. Preparation of α,β⁃unsaturated carboxylic acid ester (methyl cinnamate) by Wittig reaction using benzaldehyde and Wittig reagent The results show that the optimal conditions for the reaction are: Wittig reagent and benzaldehyde are used as raw materials, benzene is used as a solvent, and potassium carbonate is added as an additive. The reaction is stirred at room temperature for 24 hours, and the final product methyl cinnamate is obtained in a higher yield (86%). At the same time, the configuration of the product is a trans olefin product, indicating that the method has good stereoselectivity.