The disclosure discloses a drug syringe. The drug syringe comprises: a drug container (10) defining a space and a piston (20) arranged in the space. A drug chamber (30) for accommodating a drug may be formed on a side of the piston in the space； and a constant force providing device (40) is arranged on an opposite side of the piston (20) for providing a thrust to the piston (20), pushing the piston (20) to move along an extension direction of the space, and pushing out the drug in the drug chamber (30) by changing a volume of the drug chamber (30).
