A hallmark feature of cancer is its capacity to induce the development of new blood vessels. Anti-angiogenic therapies are commonly employed to combat various types of cancer. Despite notable advancements in this field, limited efficacy and resistance remain critical challenges. While anti-angiogenic therapy primarily targets endothelial cells within the abnormal vasculature, the origins of tumor vascular endothelial cells in solid tumors remain a subject of ongoing debate. Unraveling the origins of these endothelial cells is crucial for developing more effective strategies to combat tumor angiogenesis. This review summarizes the latest findings on the origins of endothelial cells in tumor angiogenesis and explores the progress, limitations, and future directions of anti-angiogenic therapy.