The invention discloses a folic acid modified sulfobetaine-chitosan nano-granule as well as a preparation method and an application thereof. Particularly the nano-granule provided by the invention is prepared by the method comprising the following steps: (1) preparing a mixed solution containing folic acid, a dehydration condensating agent and a condensation accelerant; (2) grafting the folic acid on the sulfobetaine-chitosan; and (3) dialyzing and performing freeze-drying on the nano-granule. The folic acid modified sulfobetaine-chitosan nano-granule provided by the invention has good biocompatibility and biodegradability and strong protein resistance ability; besides, due to the introduction of the folic acid grafting, the chemotherapeutic drug coated in the sulfobetaine-chitosan nano-granule is target to a tumor cell with folate receptor high expression and the treating efficiency is increased.