The present invention relates to a fat graft injection device, which comprises: an injection unit having a connection end and a terminal; The injection unit is operated by robotic arm system in controlled speed, multiple layers, multiple lines, a storage unit connected to the injection unit; and a pump unit connected to the storage unit, wherein the storage unit is between the injection unit and contains fat grafts. Fat grafts in the storage unit are injected into the subcutaneous layer through the injection unit by the pump unit with the guiding of navigation system, thus completing the fat graft injection, with accurate and effective, manner without exhausted back and forth surgeon's arm movement.