A fat suction and graft syringe includes a negative pressure adjustment mechanism. The negative pressure state in a barrel can be maintained during a procedure only by pulling and releasing a plunger, and only by slightly rotating the plunger. The plunger can be pushed inside the barrel without being constrained by a multi-level holding plate and a single-surface rotation clip, whereby the syringe has enhanced convenience in the use and production thereof so that many practitioners accustomed to using a normal syringe can easily use the syringe without separately learning how to manipulate the syringe.