A disposable syringe, comprising: a barrel, comprising a proximal end, a distal end and a hollow interior, the hollow interior being defined by a barrel-shaped inner wall; a push rod located in the interior of the barrel and movable in the barrel, the push rod comprising a proximal end located outside the proximal end of the barrel, a distal end located in the interior of the barrel, and an axis extending through the proximal end and the distal end of the push rod, the distal end of the push rod being provided with a stop flange; a rubber piston mounted on the push rod and located at a distal side of the stop flange and configured to come in contact with the inner wall of the barrel in a liquid tight manner, characterized in that the stop flange comprises: a main body portion formed about the axis of the push rod, and a pushing and pressing portion configured to push and press the rubber piston in a direction of said axis, the pushing and pressing portion forms a cantilever structure extending from the main body portion in a direction away from the axis of the push rod, wherein the pushing and pressing portion is constructed in a way of being more likely to deform compared with the rubber piston such that when the rubber piston is stopped at the distal end of the barrel, only the pushing and pressing portion deforms as continuing to push and press the rubber piston, wherein the disposable syringe further comprises a needle seat located at the distal end of the barrel and comprising a first snap-fitting mechanism; at the distal end of the push rod is provided with a second snap-fitting mechanism located at the distal side of the rubber piston, the second snap-fitting mechanism is adapted to engage with the first snap-fitting mechanism via deformation of the pushing and pressing portion upon completion of the injection. a barrel, comprising a proximal end, a distal end and a hollow interior, the hollow interior being defined by a barrel-shaped inner wall; a push rod located in the interior of the barrel and movable in the barrel, the push rod comprising a proximal end located outside the proximal end of the barrel, a distal end located in the interior of the barrel, and an axis extending through the proximal end and the distal end of the push rod, the distal end of the push rod being provided with a stop flange; a rubber piston mounted on the push rod and located at a distal side of the stop flange and configured to come in contact with the inner wall of the barrel in a liquid tight manner, characterized in that the stop flange comprises: a main body portion formed about the axis of the push rod, and a pushing and pressing portion configured to push and press the rubber piston in a direction of said axis, the pushing and pressing portion forms a cantilever structure extending from the main body portion in a direction away from the axis of the push rod, wherein the pushing and pressing portion is constructed in a way of being more likely to deform compared with the rubber piston such that when the rubber piston is stopped at the distal end of the barrel, only the pushing and pressing portion deforms as continuing to push and press the rubber piston, wherein the disposable syringe further comprises a needle seat located at the distal end of the barrel and comprising a first snap-fitting mechanism; at the distal end of the push rod is provided with a second snap-fitting mechanism located at the distal side of the rubber piston, the second snap-fitting mechanism is adapted to engage with the first snap-fitting mechanism via deformation of the pushing and pressing portion upon completion of the injection. a main body portion formed about the axis of the push rod, and a pushing and pressing portion configured to push and press the rubber piston in a direction of said axis, the pushing and pressing portion forms a cantilever structure extending from the main body portion in a direction away from the axis of the push rod, wherein the pushing and pressing portion is constructed in a way of being more likely to deform compared with the rubber piston such that when the rubber piston is stopped at the distal end of the barrel, only the pushing and pressing portion deforms as continuing to push and press the rubber piston, wherein the disposable syringe further comprises a needle seat located at the distal end of the barrel and comprising a first snap-fitting mechanism; at the distal end of the push rod is provided with a second snap-fitting mechanism located at the distal side of the rubber piston, the second snap-fitting mechanism is adapted to engage with the first snap-fitting mechanism via deformation of the pushing and pressing portion upon completion of the injection.