Abstract: A fluid infusion apparatus (100) used for administering a medication to a patient comprises: a reservoir (101) used for storing infusion fluid; a plunger (102) located within the reservoir (101) and limiting the infusion fluid together with the reservoir (101), wherein the plunger (102) is configured to be movable along the reservoir (101); an injection button (103) operatively and synchronously moving with the plunger (102) and configured to be operable; and a displacement limiting mechanism arranged parallel to the reservoir (101), and configured to limit the plunger (102) to move for a predetermined distance within the reservoir (101) when the injection button (103) is operated, thus dispensing a predetermined amount of the fluid stored in the reservoir (101). Implementing the above apparatus reduces the overall size of the apparatus and simplifies the setting process of the injection amount, thus facilitating the administration for users.