Abstract: Advantame was a novel sweetener,3-hydroxy-4-methoxy benzal acrolein was a key intermediate to synthesize the sweetener. In this paper,3-hydroxy-4-methoxy benzal acrolein was synthesized via the reaction of 3-hydroxy-4-methoxy benzaldehyde and acetaldehyde under strong alkaline condition. The mathematical model of the yield of intermediate with reaction temperature,aldehyde dropwise time and alkali concentration was established by response surface methodology. Through this model,optimum synthetic process parameters were determined. Compositions of the products were characterized by UV,FTIR,MS and XRD. Results showed that the optimized reaction conditions were 2 h,-5℃ and 12% for reaction temperature,aldehyde dropwise time and alkali concentration. Under these conditions,the intermediate productivity could reach 61.28%±1.37%,which was accordance with the predicted data(64.75%). The synthetic product was the intermediate of advantame through the analysis of UV,FTIR,MS and XRD.