Abstract: The present invention relates to an imidazo isoindole derivative, a preparation method therefor and a medical use thereof. In particular, the present invention relates to the imidazo isoindole derivative as shown in the formula (I), a preparation method and pharmaceutical composition containing the derivative, and a use thereof for treating diseases with a pathological characteristic of the IDO-mediated tryptophan metabolic pathways. The diseases comprise cancers, Alzheimer's disease, autoimmune diseases, depression, anxiety disorders, cataracts, psychological disorders and AIDS, wherein the substituents in the formula (I) are the same as those defined in the specification.