The invention belongs to the field of medicine, and particularly relates to an imidazo isoindole IDO1 compound with structural characteristics of the formula (I) shown in the description as well as a three-dimensional isomer or a pharmaceutically acceptable salt thereof, a preparation method thereof and application thereof as an indoleamine 2,3-dioxygenase 1 (IDO1) inhibitor. An experiment result shows that the compound of the invention has a significant inhibition effect for the activity of IDO1, can effectively promote the proliferation of cells T, prevents initial cells T from being differentiated into adjustable cells T, can invert IDO1 mediating immunosuppression, can be used for treating relevant diseases with pathological features of an IDO1 mediating kynurenine metabolic way including cancers, virus infection, neurodegenerative diseases, cataracts, organ transplant rejection, depression, autoimmune diseases and the like.