The invention discloses a microwave synthesis method for cinnamic acid and application of the cinnamic acid in essence. The microwave synthesis method includes the steps that (1) benzaldehyde and acetic anhydride are mixed, anhydrous potassium carbonate is added, the mixture is reacted for a period of time under the microwave condition, then water and sodium carbonate are added, and steam distillation is then conducted till oil drops do not exist in distilled liquid; (2) acidification is conducted, active carbon is added into the coarse materials, the mixture is subjected to standing for 3 minutes to 5 minutes under the microwave condition, the mixture is filtered and acidulated with concentrated hydrochloric acid, then crystallization is conducted, and finally the target product, namely the cinnamic acid is obtained. When serving as raw materials for concocting apples and cherries, the obtained cinnamic acid can be used as the apple essence, the cherry essence, the fruit essence and the floral essence for mixing; when serving as aroma mixtures, the obtained cinnamic acid is used for soap, shampoo, washing powder and daily cosmetics.