The invention discloses a preparation method of benzaldehyde from cinnamaldehyde by continuous catalytic ozone oxidation, which comprises the following steps: by using cinnamaldehyde or cassia oil as the raw material, adding a mixed solution of 50g cinnamaldehyde and anhydrous ethanol into a continuous ozonization reactor, adding 0.5-5.0% of one or more of MnO2, ZnO, Fe2O3 and CaO as a catalyst, introducing 0.05-0.85g of ozone to every gram of cinnamaldehyde per hour at -5-20 DEG C to carry out ozonization reaction for 10 minutes, continuously introducing the cinnamaldehyde-anhydrous ethanol mixed solution at the rate of 50-100g.h<-1>.gcat<-1> to continuously react to obtain a liquid-phase product, and distilling the liquid-phase product in a molecular distillation device at certain temperature under certain pressure to obtain the higher-purity benzaldehyde. The method has the advantages of simple technique, green reaction process, favorable selectivity and high benzaldehyde yield, can maintain the nature of the benzaldehyde, and can implement continuous production of natural benzaldehyde.