Abstract: Hydrazine hydrate is a high-efficiency and environmentally friendly chemical raw material. In recent years, it has attracted much attention and been widely used in various fields. This paper systematically summarizes its applications in the synthesis of important pharmaceutical intermediates such as methylhydrazine, triazole, sodium azide, aminourea hydrochloride, thiadiazoles, and pyrazoles. It also categorically introduces its specific application scenarios in the production of downstream pharmaceutical active pharmaceutical ingredients (APIs), including antineoplastic drugs, antihypertensive drugs, and antibacterial drugs.