Abstract: Disclosed are a heterocyclic compound for an immune checkpoint inhibitor capable of blocking a VISTA signaling pathway, and a preparation method therefor and a use thereof. The compound is as represented by formula I. The compound has a novel structure, can be formulated for oral administration, overcomes the treatment defects and drug resistance of monoclonal antibody-based immune checkpoint inhibitors, can be used to prepare a small molecule inhibitor easily, and is convenient for industrial production.