The invention relates to a piston of liquid container, which comprises: a liquid storing part or main body with outer cylinder, wherein the piston is used as the bottom inside the container: when the internal pressure changes, the piston can contact the internal circumference of container of outer cylinder to slide; the piston has one couple of sealing part on the external circumference, which contacts the internal circumference of outer cylinder, while said couple of sealing parts are arranged along the axle of outer cylinder, formed by round sections, polygon sections or sharp sections. |