The invention relates to the field of medical chemistry and particularly relates to phenoxy alkyl piperazine compounds (I) or (II), a preparation method thereof, a medicinal preparation containing the same and medicinal use thereof. Ar, L and R are defined in the description. Pharmacological tests prove that the compounds have certain blocking activity for voltage-gated potassium channels. Therefore, the compounds and the pharmaceutical preparations of the compounds can be used for treating series of diseases caused by dysfunction of potassium channels, such as arrhythmia and hypoxicischemic brain damage.