The invention relates to the medical field and discloses dihydrocoumarin derivatives which are compounds shown in formula I or pharmaceutically acceptable salts of the compounds in formula I. The compounds are prepared from substitute 7-hydroxyl dihydrocoumarin and substitute benzyl bromide through nucleophilic substitution. The dihydrocoumarin derivative MAO (monoamine oxidase) has high inhabitation activity, is a selective MAO-B inhibitor, has the IC50 value at the nanomole level, has high selectivity index and can be used for preparing the MAO-B inhibitor or drugs for treating central nervous system degenerative diseases, particularly drugs for treating the Parkinson's disease or the Alzheimer's disease.