Abstract: In recent years, immunotherapy, represented by immune checkpoint inhibitors, has achieved great success as an anti-tumor therapy. Oncolytic virus (OV) therapy is a new and promising approach for treating tumors, and it may be the next important breakthrough in the field of cancer treatment. OVs are natural or genetically modified viruses that are constructed to selectively replicate only in cancer cells. They directly lyse and kill cancer cells without damaging normal cells. Unlike therapy using a viral gene vector as the active drug reagent, OVs rely on themselves to replicate in and lyse tumor cells specifically. Moreover, the viral progeny released after cell lysis can infect surrounding tumor cells. With the advancements in molecular biology, virology, immunology, genetic engineering, and other disciplines, more and more research has been focusing on OV therapy, providing us with a better understanding of the molecular mechanisms involved in tumorigenesis and viral replication and regulation. This review mainly introduces the anti-tumor and clinical applications of OVs when used alone or combined with chemotherapy, radiotherapy, and immunotherapy.