Abstract: It has been proved in our experiments that (1) Dihydrocoumarin can be formed from the reaction between coumarin and tetralin; (2) Dihydrocoumarin is rather stable, but it is able to react producting other products on certain conditions. The results of analyses of the intermediates and products of reactions using chromatograph-mass spectrum, nuclear magnetic resonance and infra-red spectrograph are given. A proof that most of the steps for the reaction of Dihydrocoumarin are consecutive has been given from kinetic experiments and analytical results of the products. A mechanism for the reaction has been suggested which can reasonably explain all the experimental results.