The invention discloses a compound having the following general formula (I), wherein K is selected from a cycloalkane group shown in the following formula. The invention also discloses an indoleamine-2,3-dioxygenase inhibitor comprising the compound and an application of the compound in preparation of drugs for treating cancer. The compound of the invention can effectively inhibit cell proliferation, has a good therapeutic effect on various diseases such as cancer, has significant therapeutic effects on breast cancer, cervical cancer, colon cancer, lung cancer, stomach cancer, rectal cancer, pancreatic cancer, brain cancer, skin cancer, oral cancer, prostatic cancer, bone cancer, kidney cancer, ovarian cancer, bladder cancer, liver cancer, fallopian tube tumor, ovarian tumor, peritoneal tumor, stage IV melanoma, glioma, glioblastoma, hepatocellular carcinoma, mastoid renal tumor, head and neck tumor, leukemia, lymphoma, myeloma, non-small cell lung cancer, and the like, and has very broad application prospects.