A multi-stage electric gas pump , comprising: an eccentric shaft including a main body having a longitudinal axis, a first eccentric portion , and a second eccentric portion, wherein the first eccentric portion and the second eccentric portion are fixed on the main body , the eccentric shaft is driven by a driving mechanism to produce a first circular movement of the first eccentric portion around the longitudinal axis and a second circular movement of the second eccentric portion around the longitudinal axis, and the second circular movement is synchronized with the first circular movement; a first cylinder including a first chamber and a first piston rod , the first piston rod being connected to the first eccentric portion ; a second cylinder in fluid communication with the first cylinder , the second cylinder including a second chamber and a second piston rod , the second piston rod being connected to the first eccentric portion ; and a third cylinder in fluid communication with the second cylinder , the third cylinder including a third piston rod and a third chamber , the third piston rod being connected to the second eccentric portion , characterised in that : the first piston rod and the second piston rod are connected to each other, such that an orientation of the first piston rod is always opposite to an orientation of the second piston rod ; and the third piston rod is parallel to the first piston rod and the second piston rod , and an orientation of the third piston rod and the orientation of the second piston rod are always the same. an eccentric shaft including a main body having a longitudinal axis, a first eccentric portion , and a second eccentric portion, wherein the first eccentric portion and the second eccentric portion are fixed on the main body , the eccentric shaft is driven by a driving mechanism to produce a first circular movement of the first eccentric portion around the longitudinal axis and a second circular movement of the second eccentric portion around the longitudinal axis, and the second circular movement is synchronized with the first circular movement; a first cylinder including a first chamber and a first piston rod , the first piston rod being connected to the first eccentric portion ; a second cylinder in fluid communication with the first cylinder , the second cylinder including a second chamber and a second piston rod , the second piston rod being connected to the first eccentric portion ; and a third cylinder in fluid communication with the second cylinder , the third cylinder including a third piston rod and a third chamber , the third piston rod being connected to the second eccentric portion , characterised in that : the first piston rod and the second piston rod are connected to each other, such that an orientation of the first piston rod is always opposite to an orientation of the second piston rod ; and the third piston rod is parallel to the first piston rod and the second piston rod , and an orientation of the third piston rod and the orientation of the second piston rod are always the same. the first piston rod and the second piston rod are connected to each other, such that an orientation of the first piston rod is always opposite to an orientation of the second piston rod ; and the third piston rod is parallel to the first piston rod and the second piston rod , and an orientation of the third piston rod and the orientation of the second piston rod are always the same. <EOS>